Add a flag field to PP_CompletionCallback to control if the callback should

always be invoked asynchronously on success or error or skipped if the
operation can complete synchronously without blocking. Keep the default
behavior as-is  until clients update their code. Bump revisions of all
interfaces that take callbacks as args. Update browser interface function
implementations and C++ layer to force callbacks if sync option is not set.
Change ppapi/tests to run tests involving callbacks with both flag options.

BUG=79376
TEST=ppapi_tests + bots
Review URL: http://codereview.chromium.org/6899055

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@91205 0039d316-1c4b-4281-b951-d872f2087c98

85 files changed, 856 insertions, 365 deletions

diff --git a/chrome/test/nacl_test_injection/buildbot_nacl_integration.py b/chrome/test/nacl_test_injection/buildbot_nacl_integration.py
index fbbcf53..3800d9b 100755
--- a/chrome/test/nacl_test_injection/buildbot_nacl_integration.py
+++ b/chrome/test/nacl_test_injection/buildbot_nacl_integration.py
@@ -23,7 +23,7 @@ def Main():
 
     # Uncomment the following line if there is skew in the PPAPI interface
     # and the tests are failing.  Comment out once the issues are resolved.
-    # return
+    return
 
   script_dir = os.path.dirname(os.path.abspath(__file__))
   test_dir = os.path.dirname(script_dir)
diff --git a/ppapi/c/dev/ppb_directory_reader_dev.h b/ppapi/c/dev/ppb_directory_reader_dev.h
index 41b7299..94e1e12 100644
--- a/ppapi/c/dev/ppb_directory_reader_dev.h
+++ b/ppapi/c/dev/ppb_directory_reader_dev.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -19,8 +19,8 @@ struct PP_DirectoryEntry_Dev {
 };
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_DirectoryEntry_Dev, 8);
 
-#define PPB_DIRECTORYREADER_DEV_INTERFACE_0_4 "PPB_DirectoryReader(Dev);0.4"
-#define PPB_DIRECTORYREADER_DEV_INTERFACE PPB_DIRECTORYREADER_DEV_INTERFACE_0_4
+#define PPB_DIRECTORYREADER_DEV_INTERFACE_0_5 "PPB_DirectoryReader(Dev);0.5"
+#define PPB_DIRECTORYREADER_DEV_INTERFACE PPB_DIRECTORYREADER_DEV_INTERFACE_0_5
 
 struct PPB_DirectoryReader_Dev {
   // Creates a DirectoryReader for the given directory.  Upon success, the
@@ -56,4 +56,3 @@ struct PPB_DirectoryReader_Dev {
 };
 
 #endif  /* PPAPI_C_DEV_PPB_DIRECTORY_READER_DEV_H_ */
-
diff --git a/ppapi/c/dev/ppb_file_chooser_dev.h b/ppapi/c/dev/ppb_file_chooser_dev.h
index e0c010f..27080fe 100644
--- a/ppapi/c/dev/ppb_file_chooser_dev.h
+++ b/ppapi/c/dev/ppb_file_chooser_dev.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -31,8 +31,8 @@ struct PP_FileChooserOptions_Dev {
   const char* accept_mime_types;
 };
 
-#define PPB_FILECHOOSER_DEV_INTERFACE_0_3 "PPB_FileChooser(Dev);0.3"
-#define PPB_FILECHOOSER_DEV_INTERFACE PPB_FILECHOOSER_DEV_INTERFACE_0_3
+#define PPB_FILECHOOSER_DEV_INTERFACE_0_4 "PPB_FileChooser(Dev);0.4"
+#define PPB_FILECHOOSER_DEV_INTERFACE PPB_FILECHOOSER_DEV_INTERFACE_0_4
 
 struct PPB_FileChooser_Dev {
   // Creates a file chooser dialog with the specified options.  The chooser is
diff --git a/ppapi/c/dev/ppb_file_io_dev.h b/ppapi/c/dev/ppb_file_io_dev.h
index 0b08712..4ffd282 100644
--- a/ppapi/c/dev/ppb_file_io_dev.h
+++ b/ppapi/c/dev/ppb_file_io_dev.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -39,8 +39,8 @@ typedef enum {
 } PP_FileOpenFlags_Dev;
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_FileOpenFlags_Dev, 4);
 
-#define PPB_FILEIO_DEV_INTERFACE_0_3 "PPB_FileIO(Dev);0.3"
-#define PPB_FILEIO_DEV_INTERFACE PPB_FILEIO_DEV_INTERFACE_0_3
+#define PPB_FILEIO_DEV_INTERFACE_0_4 "PPB_FileIO(Dev);0.4"
+#define PPB_FILEIO_DEV_INTERFACE PPB_FILEIO_DEV_INTERFACE_0_4
 
 // Use this interface to operate on a regular file (PP_FileType_Regular).
 struct PPB_FileIO_Dev {
@@ -117,4 +117,3 @@ struct PPB_FileIO_Dev {
 };
 
 #endif  /* PPAPI_C_DEV_PPB_FILE_IO_DEV_H_ */
-
diff --git a/ppapi/c/dev/ppb_file_io_trusted_dev.h b/ppapi/c/dev/ppb_file_io_trusted_dev.h
index d3f7c38..ed73a6c 100644
--- a/ppapi/c/dev/ppb_file_io_trusted_dev.h
+++ b/ppapi/c/dev/ppb_file_io_trusted_dev.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -10,8 +10,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_FILEIOTRUSTED_DEV_INTERFACE_0_2 "PPB_FileIOTrusted(Dev);0.2"
-#define PPB_FILEIOTRUSTED_DEV_INTERFACE PPB_FILEIOTRUSTED_DEV_INTERFACE_0_2
+#define PPB_FILEIOTRUSTED_DEV_INTERFACE_0_3 "PPB_FileIOTrusted(Dev);0.3"
+#define PPB_FILEIOTRUSTED_DEV_INTERFACE PPB_FILEIOTRUSTED_DEV_INTERFACE_0_3
 
 // Available only to trusted implementations.
 struct PPB_FileIOTrusted_Dev {
@@ -45,4 +45,3 @@ struct PPB_FileIOTrusted_Dev {
 };
 
 #endif  /* PPAPI_C_DEV_PPB_FILE_IO_TRUSTED_DEV_H_ */
-
diff --git a/ppapi/c/dev/ppb_file_ref_dev.h b/ppapi/c/dev/ppb_file_ref_dev.h
index 61e60dc..05b3d9c 100644
--- a/ppapi/c/dev/ppb_file_ref_dev.h
+++ b/ppapi/c/dev/ppb_file_ref_dev.h
@@ -13,8 +13,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_FILEREF_DEV_INTERFACE_0_7 "PPB_FileRef(Dev);0.7"
-#define PPB_FILEREF_DEV_INTERFACE PPB_FILEREF_DEV_INTERFACE_0_7
+#define PPB_FILEREF_DEV_INTERFACE_0_8 "PPB_FileRef(Dev);0.8"
+#define PPB_FILEREF_DEV_INTERFACE PPB_FILEREF_DEV_INTERFACE_0_8
 
 // A FileRef is a "weak pointer" to a file in a file system.  It contains a
 // PP_FileSystemType identifier and a file path string.
@@ -79,4 +79,3 @@ struct PPB_FileRef_Dev {
 };
 
 #endif  /* PPAPI_C_DEV_PPB_FILE_REF_DEV_H_ */
-
diff --git a/ppapi/c/dev/ppb_file_system_dev.h b/ppapi/c/dev/ppb_file_system_dev.h
index f64236c..ba1e517 100644
--- a/ppapi/c/dev/ppb_file_system_dev.h
+++ b/ppapi/c/dev/ppb_file_system_dev.h
@@ -14,8 +14,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_FILESYSTEM_DEV_INTERFACE_0_5 "PPB_FileSystem(Dev);0.5"
-#define PPB_FILESYSTEM_DEV_INTERFACE PPB_FILESYSTEM_DEV_INTERFACE_0_5
+#define PPB_FILESYSTEM_DEV_INTERFACE_0_6 "PPB_FileSystem(Dev);0.6"
+#define PPB_FILESYSTEM_DEV_INTERFACE PPB_FILESYSTEM_DEV_INTERFACE_0_6
 
 struct PPB_FileSystem_Dev {
   /** Creates a filesystem object of the given type. */
@@ -45,4 +45,3 @@ struct PPB_FileSystem_Dev {
 };
 
 #endif  /* PPAPI_C_DEV_PPB_FILE_SYSTEM_DEV_H_ */
-
diff --git a/ppapi/c/dev/ppb_graphics_3d_dev.h b/ppapi/c/dev/ppb_graphics_3d_dev.h
index 63826c8..6e53328 100644
--- a/ppapi/c/dev/ppb_graphics_3d_dev.h
+++ b/ppapi/c/dev/ppb_graphics_3d_dev.h
@@ -31,8 +31,8 @@
 // // Shutdown.
 // core->ReleaseResource(context);
 
-#define PPB_GRAPHICS_3D_DEV_INTERFACE_0_4 "PPB_Graphics3D(Dev);0.4"
-#define PPB_GRAPHICS_3D_DEV_INTERFACE PPB_GRAPHICS_3D_DEV_INTERFACE_0_4
+#define PPB_GRAPHICS_3D_DEV_INTERFACE_0_5 "PPB_Graphics3D(Dev);0.5"
+#define PPB_GRAPHICS_3D_DEV_INTERFACE PPB_GRAPHICS_3D_DEV_INTERFACE_0_5
 
 struct PPB_Graphics3D_Dev {
   // TODO(alokp): Do these functions need module argument?
@@ -226,4 +226,3 @@ struct PPB_Graphics3D_Dev {
 };
 
 #endif  /* PPAPI_C_DEV_PPB_GRAPHICS_3D_DEV_H_ */
-
diff --git a/ppapi/c/dev/ppb_layer_compositor_dev.h b/ppapi/c/dev/ppb_layer_compositor_dev.h
index 1ee4594..1d3ee37 100644
--- a/ppapi/c/dev/ppb_layer_compositor_dev.h
+++ b/ppapi/c/dev/ppb_layer_compositor_dev.h
@@ -11,7 +11,9 @@
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_size.h"
 
-#define PPB_LAYER_COMPOSITOR_DEV_INTERFACE "PPB_LayerCompositor(Dev);0.1"
+#define PPB_LAYER_COMPOSITOR_DEV_INTERFACE_0_2 "PPB_LayerCompositor(Dev);0.2"
+#define PPB_LAYER_COMPOSITOR_DEV_INTERFACE \
+    PPB_LAYER_COMPOSITOR_DEV_INTERFACE_0_2
 
 // PPB_LayerCompositor allows multiple layers of PPB_Surface3D and
 // PPB_VideoLayer be bound to a plugin instance.
diff --git a/ppapi/c/dev/ppb_surface_3d_dev.h b/ppapi/c/dev/ppb_surface_3d_dev.h
index 1eb5057..47b47ef 100644
--- a/ppapi/c/dev/ppb_surface_3d_dev.h
+++ b/ppapi/c/dev/ppb_surface_3d_dev.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -12,8 +12,8 @@
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_resource.h"
 
-#define PPB_SURFACE_3D_DEV_INTERFACE_0_1 "PPB_Surface3D(Dev);0.1"
-#define PPB_SURFACE_3D_DEV_INTERFACE PPB_SURFACE_3D_DEV_INTERFACE_0_1
+#define PPB_SURFACE_3D_DEV_INTERFACE_0_2 "PPB_Surface3D(Dev);0.2"
+#define PPB_SURFACE_3D_DEV_INTERFACE PPB_SURFACE_3D_DEV_INTERFACE_0_2
 
 struct PPB_Surface3D_Dev {
   // Creates a render surface and returns a handle to it.
diff --git a/ppapi/c/dev/ppb_transport_dev.h b/ppapi/c/dev/ppb_transport_dev.h
index 5b303e2..bc3a8cd 100644
--- a/ppapi/c/dev/ppb_transport_dev.h
+++ b/ppapi/c/dev/ppb_transport_dev.h
@@ -13,8 +13,8 @@
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/c/pp_var.h"
 
-#define PPB_TRANSPORT_DEV_INTERFACE_0_4 "PPB_Transport;0.4"
-#define PPB_TRANSPORT_DEV_INTERFACE PPB_TRANSPORT_DEV_INTERFACE_0_4
+#define PPB_TRANSPORT_DEV_INTERFACE_0_5 "PPB_Transport;0.5"
+#define PPB_TRANSPORT_DEV_INTERFACE PPB_TRANSPORT_DEV_INTERFACE_0_5
 
 struct PPB_Transport_Dev {
   // Creates a new transport object with the specified name using the
diff --git a/ppapi/c/pp_completion_callback.h b/ppapi/c/pp_completion_callback.h
index 248dedc..bc7074a 100644
--- a/ppapi/c/pp_completion_callback.h
+++ b/ppapi/c/pp_completion_callback.h
@@ -21,8 +21,15 @@
  */
 
 /**
- * PP_CompletionCallback_Func defines the signature that you implement to
- * receive callbacks on asynchronous completion.
+ * PP_CompletionCallback_Func defines the function signature that you implement
+ * to receive callbacks on asynchronous completion of an operation.
+ *
+ * |user_data| is a pointer to user-specified data associated with this
+ * function at callback creation. See PP_MakeCompletionCallback() for details.
+ *
+ * |result| is the result of the operation. Non-positive values correspond to
+ * the error codes from pp_errors.h (excluding PP_OK_COMPLETIONPENDING).
+ * Positive values indicate additional information such as bytes read.
  */
 typedef void (*PP_CompletionCallback_Func)(void* user_data, int32_t result);
 /**
@@ -30,28 +37,61 @@ typedef void (*PP_CompletionCallback_Func)(void* user_data, int32_t result);
  */
 
 /**
+ *
+ * @addtogroup Enums
+ * @{
+ */
+
+/**
+ * This enumeration contains flags used to control how non-NULL callbacks are
+ * scheduled by asynchronous methods.
+ */
+typedef enum {
+  /**
+   * This flag allows any non-NULL callback to be always invoked asynchronously,
+   * on success or error, even if the operation could complete synchronously
+   * without blocking.
+   *
+   * The method taking such callback will always return PP_OK_COMPLETIONPENDING.
+   * The callback will be invoked on the main thread of PPAPI execution.
+   *
+   * TODO(polina): make this the default once all the clients use flags.
+   */
+  PP_COMPLETIONCALLBACK_FLAG_NONE = 0 << 0,
+  /**
+   * This flag allows any method taking such callback to complete synchronously
+   * and not call the callback if the operation would not block. This is useful
+   * when performance is an issue, and the operation bandwidth should not be
+   * limited to the processing speed of the message loop.
+   *
+   * On synchronous method completion, the completion result will be returned
+   * by the method itself. Otherwise, the method will return
+   * PP_OK_COMPLETIONPENDING, and the callback will be invoked asynchronously on
+   * the main thread of PPAPI execution.
+   */
+  PP_COMPLETIONCALLBACK_FLAG_OPTIONAL = 1 << 0
+} PP_CompletionCallback_Flag;
+PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_CompletionCallback_Flag, 4);
+
+
+/**
  * @addtogroup Structs
  * @{
  */
 
 /**
- * Any method that takes a PP_CompletionCallback has the option of completing
- * asynchronously if the operation would block.  Such a method should return
- * PP_OK_COMPLETIONPENDING to indicate that the method will complete
- * asynchronously and will always be invoked from the main thread of PPAPI
- * execution.  If the completion callback is NULL, then the operation will
- * block if necessary to complete its work.  PP_BlockUntilComplete() provides a
- * convenient way to specify blocking behavior. Refer to PP_BlockUntilComplete
- * for more information.
+ * Any method that takes a PP_CompletionCallback can complete asynchronously.
+ * Refer to PP_CompletionCallback_Flag for more information.
  *
- * The result parameter passes an int32_t that, if negative or equal to 0,
- * indicate if the call will completely asynchronously (the callback will be
- * called with a status code). A value greater than zero indicates additional
- * information such as bytes read.
+ * If PP_CompletionCallback_Func is NULL, the operation might block if necessary
+ * to complete the work. Refer to PP_BlockUntilComplete for more information.
+ *
+ * See PP_MakeCompletionCallback() for the description of each field.
  */
 struct PP_CompletionCallback {
   PP_CompletionCallback_Func func;
   void* user_data;
+  int32_t flags;
 };
 /**
  * @}
@@ -61,14 +101,20 @@ struct PP_CompletionCallback {
  * @addtogroup Functions
  * @{
  */
-
 /**
- * PP_MakeCompletionCallback() is used to create a PP_CompletionCallback.
+ * PP_MakeCompletionCallback() is used to create a PP_CompletionCallback
+ * without flags. If you want to alter the default callback behavior, set the
+ * flags to a bit field combination of PP_CompletionCallback_Flag's.
+ *
+ * Example:
+ *   struct PP_CompletionCallback cc = PP_MakeCompletionCallback(Foo, NULL);
+ *   cc.flags = cc.flags | PP_COMPLETIONCALLBACK_FLAG_OPTIONAL;
+ *
+ * @param[in] func A PP_CompletionCallback_Func to be called on completion.
+ * @param[in] user_data A pointer to user data passed to be passed to the
+ * callback function. This is optional and is typically used to help track state
+ * in case of multiple pending callbacks.
  *
- * @param[in] func A PP_CompletionCallback_Func that will be called.
- * @param[in] user_data A pointer to user data passed to your callback
- * function. This is optional and is typically used to help track state
- * when you may have multiple callbacks pending.
  * @return A PP_CompletionCallback structure.
  */
 PP_INLINE struct PP_CompletionCallback PP_MakeCompletionCallback(
@@ -77,6 +123,27 @@ PP_INLINE struct PP_CompletionCallback PP_MakeCompletionCallback(
   struct PP_CompletionCallback cc;
   cc.func = func;
   cc.user_data = user_data;
+  /* TODO(polina): switch the default to PP_COMPLETIONCALLBACK_FLAG_NONE. */
+  cc.flags = PP_COMPLETIONCALLBACK_FLAG_OPTIONAL;
+  return cc;
+}
+
+/**
+ * PP_MakeOptionalCompletionCallback() is used to create a PP_CompletionCallback
+ * with PP_COMPLETIONCALLBACK_FLAG_OPTIONAL set.
+ *
+ * @param[in] func A PP_CompletionCallback_Func to be called on completion.
+ * @param[in] user_data A pointer to user data passed to be passed to the
+ * callback function. This is optional and is typically used to help track state
+ * in case of multiple pending callbacks.
+ *
+ * @return A PP_CompletionCallback structure.
+ */
+PP_INLINE struct PP_CompletionCallback PP_MakeOptionalCompletionCallback(
+    PP_CompletionCallback_Func func,
+    void* user_data) {
+  struct PP_CompletionCallback cc = PP_MakeCompletionCallback(func, user_data);
+  cc.flags = cc.flags | PP_COMPLETIONCALLBACK_FLAG_OPTIONAL;
   return cc;
 }
 /**
@@ -89,17 +156,18 @@ PP_INLINE struct PP_CompletionCallback PP_MakeCompletionCallback(
  */
 
 /**
- * PP_RunCompletionCallback() is used to run a callback.
+ * PP_RunCompletionCallback() is used to run a callback. It invokes
+ * the callback function passing it user data specified on creation and
+ * completion |result|.
  *
  * @param[in] cc A pointer to a PP_CompletionCallback that will be run.
- * @param[in] res The result parameter that, if negative or equal to 0,
- * indicate if the call will completely asynchronously (the callback will be
- * called with a status code). A value greater than zero indicates additional
- * information such as bytes read.
+ * @param[in] result The result of the operation. Non-positive values correspond
+ * to the error codes from pp_errors.h (excluding PP_OK_COMPLETIONPENDING).
+ * Positive values indicate additional information such as bytes read.
  */
 PP_INLINE void PP_RunCompletionCallback(struct PP_CompletionCallback* cc,
-                                        int32_t res) {
-  cc->func(cc->user_data, res);
+                                        int32_t result) {
+  cc->func(cc->user_data, result);
 }
 
 /**
@@ -114,10 +182,10 @@ PP_INLINE void PP_RunCompletionCallback(struct PP_CompletionCallback* cc,
  /**
  * PP_BlockUntilComplete() is used in place of an actual completion callback
  * to request blocking behavior. If specified, the calling thread will block
- * until the function completes.  Blocking completion callbacks are only usable
+ * until the function completes. Blocking completion callbacks are only allowed
  * from background threads.
  *
- * @return A PP_CompletionCallback structure.
+ * @return A PP_CompletionCallback structure corresponding to a NULL callback.
  */
 PP_INLINE struct PP_CompletionCallback PP_BlockUntilComplete() {
   return PP_MakeCompletionCallback(NULL, NULL);
diff --git a/ppapi/c/ppb_core.h b/ppapi/c/ppb_core.h
index ac7b8f4..968dfcd 100644
--- a/ppapi/c/ppb_core.h
+++ b/ppapi/c/ppb_core.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -13,8 +13,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_CORE_INTERFACE_0_4 "PPB_Core;0.4"
-#define PPB_CORE_INTERFACE PPB_CORE_INTERFACE_0_4
+#define PPB_CORE_INTERFACE_0_5 "PPB_Core;0.5"
+#define PPB_CORE_INTERFACE PPB_CORE_INTERFACE_0_5
 
 /**
  * @file
@@ -139,4 +139,3 @@ struct PPB_Core {
 
 
 #endif  /* PPAPI_C_DEV_PPB_CORE_DEV_H_ */
-
diff --git a/ppapi/c/ppb_file_io.h b/ppapi/c/ppb_file_io.h
index 0f274db..92ad35b 100644
--- a/ppapi/c/ppb_file_io.h
+++ b/ppapi/c/ppb_file_io.h
@@ -39,8 +39,8 @@ typedef enum {
 } PP_FileOpenFlags;
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_FileOpenFlags, 4);
 
-#define PPB_FILEIO_INTERFACE_0_4 "PPB_FileIO;0.4"
-#define PPB_FILEIO_INTERFACE PPB_FILEIO_INTERFACE_0_4
+#define PPB_FILEIO_INTERFACE_0_5 "PPB_FileIO;0.5"
+#define PPB_FILEIO_INTERFACE PPB_FILEIO_INTERFACE_0_5
 
 // Use this interface to operate on a regular file (PP_FileType_Regular).
 struct PPB_FileIO {
@@ -117,3 +117,4 @@ struct PPB_FileIO {
 };
 
 #endif  /* PPAPI_C_PPB_FILE_IO_H_ */
+
diff --git a/ppapi/c/ppb_file_ref.h b/ppapi/c/ppb_file_ref.h
index 3f6faf7..4813d1a 100644
--- a/ppapi/c/ppb_file_ref.h
+++ b/ppapi/c/ppb_file_ref.h
@@ -13,8 +13,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_FILEREF_INTERFACE_0_8 "PPB_FileRef;0.8"
-#define PPB_FILEREF_INTERFACE PPB_FILEREF_INTERFACE_0_8
+#define PPB_FILEREF_INTERFACE_0_9 "PPB_FileRef;0.9"
+#define PPB_FILEREF_INTERFACE PPB_FILEREF_INTERFACE_0_9
 
 // A FileRef is a "weak pointer" to a file in a file system.  It contains a
 // PP_FileSystemType identifier and a file path string.
@@ -79,3 +79,4 @@ struct PPB_FileRef {
 };
 
 #endif  /* PPAPI_C_PPB_FILE_REF_H_ */
+
diff --git a/ppapi/c/ppb_file_system.h b/ppapi/c/ppb_file_system.h
index 692aa9c..07f1f78 100644
--- a/ppapi/c/ppb_file_system.h
+++ b/ppapi/c/ppb_file_system.h
@@ -14,8 +14,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_FILESYSTEM_INTERFACE_0_6 "PPB_FileSystem;0.6"
-#define PPB_FILESYSTEM_INTERFACE PPB_FILESYSTEM_INTERFACE_0_6
+#define PPB_FILESYSTEM_INTERFACE_0_7 "PPB_FileSystem;0.7"
+#define PPB_FILESYSTEM_INTERFACE PPB_FILESYSTEM_INTERFACE_0_7
 
 struct PPB_FileSystem {
   /** Creates a filesystem object of the given type. */
diff --git a/ppapi/c/ppb_graphics_2d.h b/ppapi/c/ppb_graphics_2d.h
index b08e9fc..d32ef5d 100644
--- a/ppapi/c/ppb_graphics_2d.h
+++ b/ppapi/c/ppb_graphics_2d.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2010 The Chromium Authors. All rights reserved.
+/* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -16,8 +16,8 @@ struct PP_Point;
 struct PP_Rect;
 struct PP_Size;
 
-#define PPB_GRAPHICS_2D_INTERFACE_0_3 "PPB_Graphics2D;0.3"
-#define PPB_GRAPHICS_2D_INTERFACE PPB_GRAPHICS_2D_INTERFACE_0_3
+#define PPB_GRAPHICS_2D_INTERFACE_0_4 "PPB_Graphics2D;0.4"
+#define PPB_GRAPHICS_2D_INTERFACE PPB_GRAPHICS_2D_INTERFACE_0_4
 
 /**
  * @file
@@ -231,4 +231,3 @@ struct PPB_Graphics2D {
  * @}
  */
 #endif  /* PPAPI_C_PPB_GRAPHICS_2D_H_ */
-
diff --git a/ppapi/c/ppb_url_loader.h b/ppapi/c/ppb_url_loader.h
index 6ff753b..afbee22 100644
--- a/ppapi/c/ppb_url_loader.h
+++ b/ppapi/c/ppb_url_loader.h
@@ -12,8 +12,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_URLLOADER_INTERFACE_0_1 "PPB_URLLoader;0.1"
-#define PPB_URLLOADER_INTERFACE PPB_URLLOADER_INTERFACE_0_1
+#define PPB_URLLOADER_INTERFACE_0_2 "PPB_URLLoader;0.2"
+#define PPB_URLLOADER_INTERFACE PPB_URLLOADER_INTERFACE_0_2
 
 /**
  * @file
@@ -216,4 +216,3 @@ struct PPB_URLLoader {
  */
 
 #endif  /* PPAPI_C_PPB_URL_LOADER_H_ */
-
diff --git a/ppapi/c/private/ppb_flash_menu.h b/ppapi/c/private/ppb_flash_menu.h
index 7fc62e5..d7cbf4d 100644
--- a/ppapi/c/private/ppb_flash_menu.h
+++ b/ppapi/c/private/ppb_flash_menu.h
@@ -10,7 +10,7 @@
 #include "ppapi/c/pp_point.h"
 #include "ppapi/c/pp_resource.h"
 
-#define PPB_FLASH_MENU_INTERFACE "PPB_Flash_Menu;1"
+#define PPB_FLASH_MENU_INTERFACE "PPB_Flash_Menu;0.2"
 
 struct PP_CompletionCallback;
 
diff --git a/ppapi/c/private/ppb_flash_net_connector.h b/ppapi/c/private/ppb_flash_net_connector.h
index 2cc25bb..9f342fc 100644
--- a/ppapi/c/private/ppb_flash_net_connector.h
+++ b/ppapi/c/private/ppb_flash_net_connector.h
@@ -10,7 +10,7 @@
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/private/ppb_flash_file.h"  // For |PP_FileHandle|.
 
-#define PPB_FLASH_NETCONNECTOR_INTERFACE "PPB_Flash_NetConnector;0.1"
+#define PPB_FLASH_NETCONNECTOR_INTERFACE "PPB_Flash_NetConnector;0.2"
 
 // This is an opaque type holding a network address.
 struct PP_Flash_NetAddress {
diff --git a/ppapi/c/trusted/ppb_audio_trusted.h b/ppapi/c/trusted/ppb_audio_trusted.h
index 49c947c..cac02f2 100644
--- a/ppapi/c/trusted/ppb_audio_trusted.h
+++ b/ppapi/c/trusted/ppb_audio_trusted.h
@@ -9,7 +9,7 @@
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_resource.h"
 
-#define PPB_AUDIO_TRUSTED_INTERFACE "PPB_AudioTrusted;0.5"
+#define PPB_AUDIO_TRUSTED_INTERFACE "PPB_AudioTrusted;0.6"
 
 /**
  * This interface is to be used by proxy implementations.  All
@@ -47,4 +47,3 @@ struct PPB_AudioTrusted {
 };
 
 #endif  /* PPAPI_C_PPB_AUDIO_TRUSTED_H_ */
-
diff --git a/ppapi/c/trusted/ppb_broker_trusted.h b/ppapi/c/trusted/ppb_broker_trusted.h
index 84fb924..5cf091f 100644
--- a/ppapi/c/trusted/ppb_broker_trusted.h
+++ b/ppapi/c/trusted/ppb_broker_trusted.h
@@ -10,7 +10,7 @@
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_resource.h"
 
-#define PPB_BROKER_TRUSTED_INTERFACE "PPB_BrokerTrusted;0.1"
+#define PPB_BROKER_TRUSTED_INTERFACE "PPB_BrokerTrusted;0.2"
 
 /**
  * @file
diff --git a/ppapi/c/trusted/ppb_file_io_trusted.h b/ppapi/c/trusted/ppb_file_io_trusted.h
index 44e6e43..766ed3f 100644
--- a/ppapi/c/trusted/ppb_file_io_trusted.h
+++ b/ppapi/c/trusted/ppb_file_io_trusted.h
@@ -10,8 +10,8 @@
 
 struct PP_CompletionCallback;
 
-#define PPB_FILEIOTRUSTED_INTERFACE_0_3 "PPB_FileIOTrusted;0.3"
-#define PPB_FILEIOTRUSTED_INTERFACE PPB_FILEIOTRUSTED_INTERFACE_0_3
+#define PPB_FILEIOTRUSTED_INTERFACE_0_4 "PPB_FileIOTrusted;0.4"
+#define PPB_FILEIOTRUSTED_INTERFACE PPB_FILEIOTRUSTED_INTERFACE_0_4
 
 // Available only to trusted implementations.
 struct PPB_FileIOTrusted {
@@ -45,3 +45,4 @@ struct PPB_FileIOTrusted {
 };
 
 #endif  /* PPAPI_C_PPB_FILE_IO_TRUSTED_H_ */
+
diff --git a/ppapi/cpp/completion_callback.h b/ppapi/cpp/completion_callback.h
index 92403f3..6438c07 100644
--- a/ppapi/cpp/completion_callback.h
+++ b/ppapi/cpp/completion_callback.h
@@ -6,6 +6,7 @@
 #define PPAPI_CPP_COMPLETION_CALLBACK_H_
 
 #include "ppapi/c/pp_completion_callback.h"
+#include "ppapi/c/pp_errors.h"
 #include "ppapi/cpp/logging.h"
 #include "ppapi/cpp/non_thread_safe_ref_count.h"
 
@@ -27,6 +28,14 @@ class CompletionCallback {
     cc_ = PP_MakeCompletionCallback(func, user_data);
   }
 
+  CompletionCallback(PP_CompletionCallback_Func func, void* user_data,
+                     int32_t flags) {
+    cc_ = PP_MakeCompletionCallback(func, user_data);
+    cc_.flags = flags;
+  }
+
+  void set_flags(int32_t flags) { cc_.flags = flags; }
+
   // Call this method to explicitly run the CompletionCallback.  Normally, the
   // system runs a CompletionCallback after an asynchronous operation
   // completes, but programs may wish to run the CompletionCallback manually
@@ -36,7 +45,34 @@ class CompletionCallback {
     PP_RunCompletionCallback(&cc_, result);
   }
 
+  bool IsOptional() const {
+    return (cc_.func == NULL ||
+            (cc_.flags & PP_COMPLETIONCALLBACK_FLAG_OPTIONAL) != 0);
+  }
+
   const PP_CompletionCallback& pp_completion_callback() const { return cc_; }
+  int32_t flags() const { return cc_.flags; }
+
+  // Use this when implementing functions taking callbacks.
+  // If the callback is required and |result| indicates that it has not
+  // been scheduled, it will be forced on the main thread.
+  //
+  // EXAMPLE USAGE:
+  //
+  // int32_t OpenURL(pp::URLLoader* loader,
+  //                 pp::URLRequestInfo* url_request_info,
+  //                 const CompletionCallback& cc) {
+  //   if (loader == NULL || url_request_info == NULL)
+  //     return cc.MayForce(PP_ERROR_BADRESOURCE);
+  //   return loader->Open(*loader, *url_request_info, cc);
+  // }
+  //
+  int32_t MayForce(int32_t result) const {
+    if (result == PP_OK_COMPLETIONPENDING || IsOptional())
+      return result;
+    Module::Get()->core()->CallOnMainThread(0, *this, result);
+    return PP_OK_COMPLETIONPENDING;
+  }
 
  protected:
   PP_CompletionCallback cc_;
@@ -67,10 +103,10 @@ class CompletionCallback {
 //     }
 //
 //     void ProcessFile(const FileRef& file) {
-//       CompletionCallback cc = factory_.NewCallback(&MyHandler::DidOpen);
+//       CompletionCallback cc = factory_.NewRequiredCallback(
+//           &MyHandler::DidOpen);
 //       int32_t rv = fio_.Open(file, PP_FileOpenFlag_Read, cc);
-//       if (rv != PP_OK_COMPLETIONPENDING)
-//         cc.Run(rv);
+//       CHECK(rv == PP_OK_COMPLETIONPENDING);
 //     }
 //
 //    private:
@@ -100,7 +136,8 @@ class CompletionCallback {
 //     }
 //
 //     void ReadMore() {
-//       CompletionCallback cc = factory_.NewCallback(&MyHandler::DidRead);
+//       CompletionCallback cc =
+//           factory_.NewOptionalCallback(&MyHandler::DidRead);
 //       int32_t rv = fio_.Read(offset_, buf_, sizeof(buf_),
 //                              cc.pp_completion_callback());
 //       if (rv != PP_OK_COMPLETIONPENDING)
@@ -145,11 +182,17 @@ class CompletionCallbackFactory {
     return object_;
   }
 
-  // Allocates a new, single-use CompletionCallback.  The CompletionCallback
-  // must be run in order for the memory allocated by NewCallback to be freed.
-  // If after passing the CompletionCallback to a PPAPI method, the method does
-  // not return PP_OK_COMPLETIONPENDING, then you should manually call the
-  // CompletionCallback's Run method otherwise memory will be leaked.
+  // Methods for allocating new, single-use CompletionCallbacks.
+  // The CompletionCallback must be run in order for the memory
+  // allocated by the methods to be freed.
+  // NewRequiredCallback() creates callbacks that will always run.
+  // NewOptionalCallback() creates callbacks that might not run if the method
+  // taking them can complete synchronously. Thus, if after passing the
+  // CompletionCallback to a PPAPI method, the method does not return
+  // PP_OK_COMPLETIONPENDING, then you should manually call the
+  // CompletionCallback's Run method, or memory will be leaked.
+  // NewCallback() is equivalent to NewOptionalCallback().
+  // TODO(polina): update this comment when this is no longer true.
 
   template <typename Method>
   CompletionCallback NewCallback(Method method) {
@@ -157,6 +200,20 @@ class CompletionCallbackFactory {
     return NewCallbackHelper(Dispatcher0<Method>(method));
   }
 
+  template <typename Method>
+  CompletionCallback NewRequiredCallback(Method method) {
+    CompletionCallback cc = NewCallback(method);
+    cc.set_flags(cc.flags() & ~PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+    return cc;
+  }
+
+  template <typename Method>
+  CompletionCallback NewOptionalCallback(Method method) {
+    CompletionCallback cc = NewCallback(method);
+    cc.set_flags(cc.flags() | PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+    return cc;
+  }
+
   // A copy of "a" will be passed to "method" when the completion callback
   // runs.
   //
@@ -169,6 +226,20 @@ class CompletionCallbackFactory {
     return NewCallbackHelper(Dispatcher1<Method, A>(method, a));
   }
 
+  template <typename Method, typename A>
+  CompletionCallback NewRequiredCallback(Method method, const A& a) {
+    CompletionCallback cc = NewCallback(method, a);
+    cc.set_flags(cc.flags() & ~PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+    return cc;
+  }
+
+  template <typename Method, typename A>
+  CompletionCallback NewOptionalCallback(Method method, const A& a) {
+    CompletionCallback cc = NewCallback(method, a);
+    cc.set_flags(cc.flags() | PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+    return cc;
+  }
+
   // A copy of "a" and "b" will be passed to "method" when the completion
   // callback runs.
   //
@@ -181,6 +252,22 @@ class CompletionCallbackFactory {
     return NewCallbackHelper(Dispatcher2<Method, A, B>(method, a, b));
   }
 
+  template <typename Method, typename A, typename B>
+  CompletionCallback NewRequiredCallback(Method method, const A& a,
+                                         const B& b) {
+    CompletionCallback cc = NewCallback(method, a, b);
+    cc.set_flags(cc.flags() & ~PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+    return cc;
+  }
+
+  template <typename Method, typename A, typename B>
+  CompletionCallback NewOptionalCallback(Method method, const A& a,
+                                         const B& b) {
+    CompletionCallback cc = NewCallback(method, a, b);
+    cc.set_flags(cc.flags() | PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+    return cc;
+  }
+
  private:
   class BackPointer {
    public:
diff --git a/ppapi/cpp/dev/directory_reader_dev.cc b/ppapi/cpp/dev/directory_reader_dev.cc
index 0b461e0b..9b616ee 100644
--- a/ppapi/cpp/dev/directory_reader_dev.cc
+++ b/ppapi/cpp/dev/directory_reader_dev.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -35,7 +35,7 @@ DirectoryReader_Dev::DirectoryReader_Dev(const DirectoryReader_Dev& other)
 int32_t DirectoryReader_Dev::GetNextEntry(DirectoryEntry_Dev* entry,
                                           const CompletionCallback& cc) {
   if (!has_interface<PPB_DirectoryReader_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_DirectoryReader_Dev>()->GetNextEntry(
       pp_resource(), &entry->data_, cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/dev/file_chooser_dev.cc b/ppapi/cpp/dev/file_chooser_dev.cc
index 1e63ec9..e0c0e62 100644
--- a/ppapi/cpp/dev/file_chooser_dev.cc
+++ b/ppapi/cpp/dev/file_chooser_dev.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -36,7 +36,7 @@ FileChooser_Dev::FileChooser_Dev(const FileChooser_Dev& other)
 
 int32_t FileChooser_Dev::Show(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileChooser_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileChooser_Dev>()->Show(
       pp_resource(), cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/dev/file_io_dev.cc b/ppapi/cpp/dev/file_io_dev.cc
index 1fc273b..586de42 100644
--- a/ppapi/cpp/dev/file_io_dev.cc
+++ b/ppapi/cpp/dev/file_io_dev.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -41,7 +41,7 @@ int32_t FileIO_Dev::Open(const FileRef_Dev& file_ref,
                          int32_t open_flags,
                          const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->Open(
       pp_resource(), file_ref.pp_resource(), open_flags,
       cc.pp_completion_callback());
@@ -50,7 +50,7 @@ int32_t FileIO_Dev::Open(const FileRef_Dev& file_ref,
 int32_t FileIO_Dev::Query(PP_FileInfo_Dev* result_buf,
                           const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->Query(
       pp_resource(), result_buf, cc.pp_completion_callback());
 }
@@ -59,7 +59,7 @@ int32_t FileIO_Dev::Touch(PP_Time last_access_time,
                           PP_Time last_modified_time,
                           const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->Touch(
       pp_resource(), last_access_time, last_modified_time,
       cc.pp_completion_callback());
@@ -70,7 +70,7 @@ int32_t FileIO_Dev::Read(int64_t offset,
                          int32_t bytes_to_read,
                          const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->Read(pp_resource(),
       offset, buffer, bytes_to_read, cc.pp_completion_callback());
 }
@@ -80,7 +80,7 @@ int32_t FileIO_Dev::Write(int64_t offset,
                           int32_t bytes_to_write,
                           const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->Write(
       pp_resource(), offset, buffer, bytes_to_write,
       cc.pp_completion_callback());
@@ -89,14 +89,14 @@ int32_t FileIO_Dev::Write(int64_t offset,
 int32_t FileIO_Dev::SetLength(int64_t length,
                           const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->SetLength(
       pp_resource(), length, cc.pp_completion_callback());
 }
 
 int32_t FileIO_Dev::Flush(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO_Dev>()->Flush(
       pp_resource(), cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/dev/file_ref_dev.cc b/ppapi/cpp/dev/file_ref_dev.cc
index a6a2acf..882adb1 100644
--- a/ppapi/cpp/dev/file_ref_dev.cc
+++ b/ppapi/cpp/dev/file_ref_dev.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -69,7 +69,7 @@ FileRef_Dev FileRef_Dev::GetParent() const {
 
 int32_t FileRef_Dev::MakeDirectory(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef_Dev>()->MakeDirectory(
       pp_resource(),
       PP_FALSE,  // make_ancestors
@@ -79,7 +79,7 @@ int32_t FileRef_Dev::MakeDirectory(const CompletionCallback& cc) {
 int32_t FileRef_Dev::MakeDirectoryIncludingAncestors(
     const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef_Dev>()->MakeDirectory(
       pp_resource(),
       PP_TRUE,  // make_ancestors
@@ -90,7 +90,7 @@ int32_t FileRef_Dev::Touch(PP_Time last_access_time,
                            PP_Time last_modified_time,
                            const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef_Dev>()->Touch(
       pp_resource(), last_access_time, last_modified_time,
       cc.pp_completion_callback());
@@ -98,7 +98,7 @@ int32_t FileRef_Dev::Touch(PP_Time last_access_time,
 
 int32_t FileRef_Dev::Delete(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef_Dev>()->Delete(
       pp_resource(), cc.pp_completion_callback());
 }
@@ -106,7 +106,7 @@ int32_t FileRef_Dev::Delete(const CompletionCallback& cc) {
 int32_t FileRef_Dev::Rename(const FileRef_Dev& new_file_ref,
                             const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef_Dev>()->Rename(
       pp_resource(), new_file_ref.pp_resource(), cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/dev/file_system_dev.cc b/ppapi/cpp/dev/file_system_dev.cc
index 6c25e23..bba49dd 100644
--- a/ppapi/cpp/dev/file_system_dev.cc
+++ b/ppapi/cpp/dev/file_system_dev.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -32,7 +32,7 @@ FileSystem_Dev::FileSystem_Dev(Instance* instance,
 int32_t FileSystem_Dev::Open(int64_t expected_size,
                              const CompletionCallback& cc) {
   if (!has_interface<PPB_FileSystem_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileSystem_Dev>()->Open(
       pp_resource(), expected_size, cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/dev/surface_3d_dev.cc b/ppapi/cpp/dev/surface_3d_dev.cc
index eab8149..9bc1430 100644
--- a/ppapi/cpp/dev/surface_3d_dev.cc
+++ b/ppapi/cpp/dev/surface_3d_dev.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -40,7 +40,7 @@ Surface3D_Dev::Surface3D_Dev(const Instance& instance,
 
 int32_t Surface3D_Dev::SwapBuffers(const CompletionCallback& cc) const {
   if (!has_interface<PPB_Surface3D_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
 
   return get_interface<PPB_Surface3D_Dev>()->SwapBuffers(
       pp_resource(),
diff --git a/ppapi/cpp/dev/transport_dev.cc b/ppapi/cpp/dev/transport_dev.cc
index 0b62829..cdbbd8c 100644
--- a/ppapi/cpp/dev/transport_dev.cc
+++ b/ppapi/cpp/dev/transport_dev.cc
@@ -38,7 +38,7 @@ bool Transport_Dev::IsWritable() {
 
 int32_t Transport_Dev::Connect(const CompletionCallback& cc) {
   if (!has_interface<PPB_Transport_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Transport_Dev>()->Connect(
       pp_resource(), cc.pp_completion_callback());
 }
@@ -46,7 +46,7 @@ int32_t Transport_Dev::Connect(const CompletionCallback& cc) {
 int32_t Transport_Dev::GetNextAddress(Var* address,
                                       const CompletionCallback& cc) {
   if (!has_interface<PPB_Transport_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   PP_Var temp_address = PP_MakeUndefined();
   int32_t ret_val = get_interface<PPB_Transport_Dev>()->GetNextAddress(
       pp_resource(), &temp_address, cc.pp_completion_callback());
@@ -64,7 +64,7 @@ int32_t Transport_Dev::ReceiveRemoteAddress(const pp::Var& address) {
 int32_t Transport_Dev::Recv(void* data, uint32_t len,
                             const CompletionCallback& cc) {
   if (!has_interface<PPB_Transport_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Transport_Dev>()->Recv(
       pp_resource(), data, len, cc.pp_completion_callback());
 }
@@ -72,7 +72,7 @@ int32_t Transport_Dev::Recv(void* data, uint32_t len,
 int32_t Transport_Dev::Send(const void* data, uint32_t len,
                             const CompletionCallback& cc) {
   if (!has_interface<PPB_Transport_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Transport_Dev>()->Send(
       pp_resource(), data, len, cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/dev/video_decoder_dev.cc b/ppapi/cpp/dev/video_decoder_dev.cc
index c8d6ff4..91e86d3 100644
--- a/ppapi/cpp/dev/video_decoder_dev.cc
+++ b/ppapi/cpp/dev/video_decoder_dev.cc
@@ -12,6 +12,7 @@
 #include "ppapi/cpp/instance.h"
 #include "ppapi/cpp/module.h"
 #include "ppapi/cpp/module_impl.h"
+#include "ppapi/thunk/common.h"
 
 namespace pp {
 
@@ -39,7 +40,7 @@ int32_t VideoDecoder_Dev::Initialize(const PP_VideoConfigElement* config,
                                      const Context3D_Dev& context,
                                      CompletionCallback callback) {
   if (!has_interface<PPB_VideoDecoder_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return callback.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_VideoDecoder_Dev>()->Initialize(
       pp_resource(), context.pp_resource(), config,
       callback.pp_completion_callback());
@@ -77,9 +78,7 @@ int32_t VideoDecoder_Dev::Decode(
     const PP_VideoBitstreamBuffer_Dev& bitstream_buffer,
     CompletionCallback callback) {
   if (!has_interface<PPB_VideoDecoder_Dev>())
-    return PP_ERROR_NOINTERFACE;
-  if (!pp_resource())
-    return PP_ERROR_BADRESOURCE;
+    return callback.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_VideoDecoder_Dev>()->Decode(
       pp_resource(), &bitstream_buffer, callback.pp_completion_callback());
 }
@@ -93,18 +92,14 @@ void VideoDecoder_Dev::ReusePictureBuffer(int32_t picture_buffer_id) {
 
 int32_t VideoDecoder_Dev::Flush(CompletionCallback callback) {
   if (!has_interface<PPB_VideoDecoder_Dev>())
-    return PP_ERROR_NOINTERFACE;
-  if (!pp_resource())
-    return PP_ERROR_BADRESOURCE;
+    return callback.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_VideoDecoder_Dev>()->Flush(
       pp_resource(), callback.pp_completion_callback());
 }
 
 int32_t VideoDecoder_Dev::Abort(CompletionCallback callback) {
   if (!has_interface<PPB_VideoDecoder_Dev>())
-    return PP_ERROR_NOINTERFACE;
-  if (!pp_resource())
-    return PP_ERROR_BADRESOURCE;
+    return callback.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_VideoDecoder_Dev>()->Abort(
       pp_resource(), callback.pp_completion_callback());
 }
diff --git a/ppapi/cpp/file_io.cc b/ppapi/cpp/file_io.cc
index ca6760b..85c3051 100644
--- a/ppapi/cpp/file_io.cc
+++ b/ppapi/cpp/file_io.cc
@@ -41,7 +41,7 @@ int32_t FileIO::Open(const FileRef& file_ref,
                      int32_t open_flags,
                      const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->Open(
       pp_resource(), file_ref.pp_resource(), open_flags,
       cc.pp_completion_callback());
@@ -50,7 +50,7 @@ int32_t FileIO::Open(const FileRef& file_ref,
 int32_t FileIO::Query(PP_FileInfo* result_buf,
                       const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->Query(
       pp_resource(), result_buf, cc.pp_completion_callback());
 }
@@ -59,7 +59,7 @@ int32_t FileIO::Touch(PP_Time last_access_time,
                       PP_Time last_modified_time,
                       const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->Touch(
       pp_resource(), last_access_time, last_modified_time,
       cc.pp_completion_callback());
@@ -70,7 +70,7 @@ int32_t FileIO::Read(int64_t offset,
                      int32_t bytes_to_read,
                      const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->Read(pp_resource(),
       offset, buffer, bytes_to_read, cc.pp_completion_callback());
 }
@@ -80,7 +80,7 @@ int32_t FileIO::Write(int64_t offset,
                       int32_t bytes_to_write,
                       const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->Write(
       pp_resource(), offset, buffer, bytes_to_write,
       cc.pp_completion_callback());
@@ -89,14 +89,14 @@ int32_t FileIO::Write(int64_t offset,
 int32_t FileIO::SetLength(int64_t length,
                           const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->SetLength(
       pp_resource(), length, cc.pp_completion_callback());
 }
 
 int32_t FileIO::Flush(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileIO>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileIO>()->Flush(
       pp_resource(), cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/file_ref.cc b/ppapi/cpp/file_ref.cc
index fdae3d8..ed98974 100644
--- a/ppapi/cpp/file_ref.cc
+++ b/ppapi/cpp/file_ref.cc
@@ -69,7 +69,7 @@ FileRef FileRef::GetParent() const {
 
 int32_t FileRef::MakeDirectory(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef>()->MakeDirectory(
       pp_resource(),
       PP_FALSE,  // make_ancestors
@@ -79,7 +79,7 @@ int32_t FileRef::MakeDirectory(const CompletionCallback& cc) {
 int32_t FileRef::MakeDirectoryIncludingAncestors(
     const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef>()->MakeDirectory(
       pp_resource(),
       PP_TRUE,  // make_ancestors
@@ -90,7 +90,7 @@ int32_t FileRef::Touch(PP_Time last_access_time,
                        PP_Time last_modified_time,
                        const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef>()->Touch(
       pp_resource(), last_access_time, last_modified_time,
       cc.pp_completion_callback());
@@ -98,7 +98,7 @@ int32_t FileRef::Touch(PP_Time last_access_time,
 
 int32_t FileRef::Delete(const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef>()->Delete(
       pp_resource(), cc.pp_completion_callback());
 }
@@ -106,7 +106,7 @@ int32_t FileRef::Delete(const CompletionCallback& cc) {
 int32_t FileRef::Rename(const FileRef& new_file_ref,
                         const CompletionCallback& cc) {
   if (!has_interface<PPB_FileRef>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileRef>()->Rename(
       pp_resource(), new_file_ref.pp_resource(), cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/file_system.cc b/ppapi/cpp/file_system.cc
index c5312bb..b5ee1f3 100644
--- a/ppapi/cpp/file_system.cc
+++ b/ppapi/cpp/file_system.cc
@@ -32,7 +32,7 @@ FileSystem::FileSystem(Instance* instance,
 int32_t FileSystem::Open(int64_t expected_size,
                          const CompletionCallback& cc) {
   if (!has_interface<PPB_FileSystem>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileSystem>()->Open(
       pp_resource(), expected_size, cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/graphics_2d.cc b/ppapi/cpp/graphics_2d.cc
index 0db5862..6a109f0 100644
--- a/ppapi/cpp/graphics_2d.cc
+++ b/ppapi/cpp/graphics_2d.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -100,7 +100,7 @@ void Graphics2D::ReplaceContents(ImageData* image) {
 
 int32_t Graphics2D::Flush(const CompletionCallback& cc) {
   if (!has_interface<PPB_Graphics2D>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Graphics2D>()->Flush(pp_resource(),
                                                 cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/paint_manager.cc b/ppapi/cpp/paint_manager.cc
index bc02016..23f66d5 100644
--- a/ppapi/cpp/paint_manager.cc
+++ b/ppapi/cpp/paint_manager.cc
@@ -153,7 +153,7 @@ void PaintManager::DoPaint() {
   if (client_->OnPaint(graphics_, update.paint_rects, update.paint_bounds)) {
     // Something was painted, schedule a flush.
     int32_t result = graphics_.Flush(
-        callback_factory_.NewCallback(&PaintManager::OnFlushComplete));
+        callback_factory_.NewOptionalCallback(&PaintManager::OnFlushComplete));
 
     // If you trigger this assertion, then your plugin has called Flush()
     // manually. When using the PaintManager, you should not call Flush, it
diff --git a/ppapi/cpp/private/flash_menu.cc b/ppapi/cpp/private/flash_menu.cc
index 8596fc9..5b78eec 100644
--- a/ppapi/cpp/private/flash_menu.cc
+++ b/ppapi/cpp/private/flash_menu.cc
@@ -36,7 +36,7 @@ int32_t Menu::Show(const Point& location,
                    int32_t* selected_id,
                    const CompletionCallback& cc) {
   if (!has_interface<PPB_Flash_Menu>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Flash_Menu>()->Show(
       pp_resource(),
       &location.pp_point(),
diff --git a/ppapi/cpp/private/flash_net_connector.cc b/ppapi/cpp/private/flash_net_connector.cc
index 8896114..05b26f2 100644
--- a/ppapi/cpp/private/flash_net_connector.cc
+++ b/ppapi/cpp/private/flash_net_connector.cc
@@ -38,7 +38,7 @@ int32_t NetConnector::ConnectTcp(const char* host,
                                  PP_Flash_NetAddress* remote_addr_out,
                                  const CompletionCallback& cc) {
   if (!has_interface<PPB_Flash_NetConnector>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Flash_NetConnector>()->ConnectTcp(
       pp_resource(),
       host, port,
@@ -52,7 +52,7 @@ int32_t NetConnector::ConnectTcpAddress(const PP_Flash_NetAddress* addr,
                                         PP_Flash_NetAddress* remote_addr_out,
                                         const CompletionCallback& cc) {
   if (!has_interface<PPB_Flash_NetConnector>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Flash_NetConnector>()->ConnectTcpAddress(
       pp_resource(),
       addr,
diff --git a/ppapi/cpp/url_loader.cc b/ppapi/cpp/url_loader.cc
index cf05f3c..65aa1f3 100644
--- a/ppapi/cpp/url_loader.cc
+++ b/ppapi/cpp/url_loader.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -49,7 +49,7 @@ URLLoader::URLLoader(const URLLoader& other) : Resource(other) {
 int32_t URLLoader::Open(const URLRequestInfo& request_info,
                         const CompletionCallback& cc) {
   if (!has_interface<PPB_URLLoader>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_URLLoader>()->Open(pp_resource(),
                                               request_info.pp_resource(),
                                               cc.pp_completion_callback());
@@ -57,7 +57,7 @@ int32_t URLLoader::Open(const URLRequestInfo& request_info,
 
 int32_t URLLoader::FollowRedirect(const CompletionCallback& cc) {
   if (!has_interface<PPB_URLLoader>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_URLLoader>()->FollowRedirect(
       pp_resource(), cc.pp_completion_callback());
 }
@@ -92,14 +92,14 @@ int32_t URLLoader::ReadResponseBody(void* buffer,
                                     int32_t bytes_to_read,
                                     const CompletionCallback& cc) {
   if (!has_interface<PPB_URLLoader>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_URLLoader>()->ReadResponseBody(
       pp_resource(), buffer, bytes_to_read, cc.pp_completion_callback());
 }
 
 int32_t URLLoader::FinishStreamingToFile(const CompletionCallback& cc) {
   if (!has_interface<PPB_URLLoader>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_URLLoader>()->FinishStreamingToFile(
       pp_resource(), cc.pp_completion_callback());
 }
diff --git a/ppapi/cpp/url_loader.h b/ppapi/cpp/url_loader.h
index 6db80f96..a83f44a 100644
--- a/ppapi/cpp/url_loader.h
+++ b/ppapi/cpp/url_loader.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -34,7 +34,7 @@ class URLResponseInfo;
 //     }
 //    private:
 //     CompletionCallback* NewCallback() {
-//       return factory_.NewCallback(&MyHandler::DidCompleteIO);
+//       return factory_.NewOptionalCallback(&MyHandler::DidCompleteIO);
 //     }
 //     URLRequestInfo MakeRequest(const char* url) {
 //       URLRequestInfo request;
diff --git a/ppapi/example/example.cc b/ppapi/example/example.cc
index 5dc3842..93696f0 100644
--- a/ppapi/example/example.cc
+++ b/ppapi/example/example.cc
@@ -107,7 +107,7 @@ class MyFetcher {
     client_ = client;
 
     pp::CompletionCallback callback =
-        callback_factory_.NewCallback(&MyFetcher::DidOpen);
+        callback_factory_.NewOptionalCallback(&MyFetcher::DidOpen);
     int rv = loader_.Open(request, callback);
     if (rv != PP_OK_COMPLETIONPENDING)
       callback.Run(rv);
@@ -124,7 +124,7 @@ class MyFetcher {
  private:
   void ReadMore() {
     pp::CompletionCallback callback =
-        callback_factory_.NewCallback(&MyFetcher::DidRead);
+        callback_factory_.NewOptionalCallback(&MyFetcher::DidRead);
     int rv = loader_.ReadResponseBody(buf_, sizeof(buf_), callback);
     if (rv != PP_OK_COMPLETIONPENDING)
       callback.Run(rv);
diff --git a/ppapi/ppapi_shared.gypi b/ppapi/ppapi_shared.gypi
index 11440a1..0b47f83 100644
--- a/ppapi/ppapi_shared.gypi
+++ b/ppapi/ppapi_shared.gypi
@@ -50,6 +50,8 @@
         'shared_impl/webkit_forwarding.cc',
         'shared_impl/webkit_forwarding.h',
 
+        'thunk/common.h',
+        'thunk/common.cc',
         'thunk/enter.h',
         'thunk/ppb_audio_api.h',
         'thunk/ppb_audio_config_api.h',
diff --git a/ppapi/proxy/ppb_audio_proxy.cc b/ppapi/proxy/ppb_audio_proxy.cc
index 22ddddd..76f3046 100644
--- a/ppapi/proxy/ppb_audio_proxy.cc
+++ b/ppapi/proxy/ppb_audio_proxy.cc
@@ -207,7 +207,7 @@ void PPB_Audio_Proxy::OnMsgCreate(PP_Instance instance_id,
     return;
 
   // Initiate opening the audio object.
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Audio_Proxy::AudioChannelConnected, *result);
   int32_t open_error = trusted_audio.object()->OpenTrusted(
       audio_config_res, callback.pp_completion_callback());
diff --git a/ppapi/proxy/ppb_broker_proxy.cc b/ppapi/proxy/ppb_broker_proxy.cc
index fd789de..37f8ba0 100644
--- a/ppapi/proxy/ppb_broker_proxy.cc
+++ b/ppapi/proxy/ppb_broker_proxy.cc
@@ -204,7 +204,7 @@ void PPB_Broker_Proxy::OnMsgCreate(PP_Instance instance,
 }
 
 void PPB_Broker_Proxy::OnMsgConnect(const HostResource& broker) {
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Broker_Proxy::ConnectCompleteInHost, broker);
 
   int32_t result = ppb_broker_target()->Connect(
diff --git a/ppapi/proxy/ppb_file_chooser_proxy.cc b/ppapi/proxy/ppb_file_chooser_proxy.cc
index 38bc058..cda175f 100644
--- a/ppapi/proxy/ppb_file_chooser_proxy.cc
+++ b/ppapi/proxy/ppb_file_chooser_proxy.cc
@@ -194,7 +194,7 @@ void PPB_FileChooser_Proxy::OnMsgCreate(PP_Instance instance,
 }
 
 void PPB_FileChooser_Proxy::OnMsgShow(const HostResource& chooser) {
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_FileChooser_Proxy::OnShowCallback, chooser);
 
   int32_t result = ppb_file_chooser_target()->Show(
diff --git a/ppapi/proxy/ppb_file_system_proxy.cc b/ppapi/proxy/ppb_file_system_proxy.cc
index c6b7caa..b95e0b9 100644
--- a/ppapi/proxy/ppb_file_system_proxy.cc
+++ b/ppapi/proxy/ppb_file_system_proxy.cc
@@ -178,7 +178,7 @@ void PPB_FileSystem_Proxy::OnMsgOpen(const HostResource& host_resource,
   if (enter.failed())
     return;
 
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_FileSystem_Proxy::OpenCompleteInHost, host_resource);
   int32_t result = enter.object()->Open(expected_size,
                                         callback.pp_completion_callback());
diff --git a/ppapi/proxy/ppb_flash_menu_proxy.cc b/ppapi/proxy/ppb_flash_menu_proxy.cc
index 0087700..c42c10e 100644
--- a/ppapi/proxy/ppb_flash_menu_proxy.cc
+++ b/ppapi/proxy/ppb_flash_menu_proxy.cc
@@ -162,7 +162,7 @@ void PPB_Flash_Menu_Proxy::OnMsgShow(const HostResource& menu,
                                      const PP_Point& location) {
   ShowRequest* request = new ShowRequest;
   request->menu = menu;
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Flash_Menu_Proxy::SendShowACKToPlugin, request);
 
   EnterHostFromHostResource<PPB_Flash_Menu_API> enter(menu);
diff --git a/ppapi/proxy/ppb_flash_net_connector_proxy.cc b/ppapi/proxy/ppb_flash_net_connector_proxy.cc
index 8a5aa41..ba2c218 100644
--- a/ppapi/proxy/ppb_flash_net_connector_proxy.cc
+++ b/ppapi/proxy/ppb_flash_net_connector_proxy.cc
@@ -265,7 +265,7 @@ void PPB_Flash_NetConnector_Proxy::OnMsgConnectTcp(
     const std::string& host,
     uint16_t port) {
   ConnectCallbackInfo* info = new ConnectCallbackInfo(resource);
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Flash_NetConnector_Proxy::OnCompleteCallbackInHost, info);
 
   EnterHostFromHostResource<PPB_Flash_NetConnector_API> enter(resource);
@@ -283,7 +283,7 @@ void PPB_Flash_NetConnector_Proxy::OnMsgConnectTcpAddress(
     const HostResource& resource,
     const std::string& net_address_as_string) {
   ConnectCallbackInfo* info = new ConnectCallbackInfo(resource);
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Flash_NetConnector_Proxy::OnCompleteCallbackInHost, info);
 
   PP_Flash_NetAddress net_address;
diff --git a/ppapi/proxy/ppb_graphics_2d_proxy.cc b/ppapi/proxy/ppb_graphics_2d_proxy.cc
index 8027956..0f8a247 100644
--- a/ppapi/proxy/ppb_graphics_2d_proxy.cc
+++ b/ppapi/proxy/ppb_graphics_2d_proxy.cc
@@ -240,7 +240,7 @@ void PPB_Graphics2D_Proxy::OnMsgReplaceContents(
 }
 
 void PPB_Graphics2D_Proxy::OnMsgFlush(const HostResource& graphics_2d) {
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Graphics2D_Proxy::SendFlushACKToPlugin, graphics_2d);
   int32_t result = ppb_graphics_2d_target()->Flush(
       graphics_2d.host_resource(), callback.pp_completion_callback());
diff --git a/ppapi/proxy/ppb_surface_3d_proxy.cc b/ppapi/proxy/ppb_surface_3d_proxy.cc
index 053fc01..c0288d0 100644
--- a/ppapi/proxy/ppb_surface_3d_proxy.cc
+++ b/ppapi/proxy/ppb_surface_3d_proxy.cc
@@ -177,7 +177,7 @@ void PPB_Surface3D_Proxy::OnMsgCreate(PP_Instance instance,
 }
 
 void PPB_Surface3D_Proxy::OnMsgSwapBuffers(const HostResource& surface_3d) {
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_Surface3D_Proxy::SendSwapBuffersACKToPlugin, surface_3d);
 
   EnterHostFromHostResource<PPB_Surface3D_API> enter(surface_3d);
diff --git a/ppapi/proxy/ppb_url_loader_proxy.cc b/ppapi/proxy/ppb_url_loader_proxy.cc
index 304e0e1..b2d6276 100644
--- a/ppapi/proxy/ppb_url_loader_proxy.cc
+++ b/ppapi/proxy/ppb_url_loader_proxy.cc
@@ -517,7 +517,7 @@ void PPB_URLLoader_Proxy::OnMsgReadResponseBody(
   // TODO(brettw) have a way to check for out-of-memory.
   info->read_buffer.resize(bytes_to_read);
 
-  CompletionCallback callback = callback_factory_.NewCallback(
+  CompletionCallback callback = callback_factory_.NewOptionalCallback(
       &PPB_URLLoader_Proxy::OnReadCallback, info);
 
   EnterHostFromHostResource<PPB_URLLoader_API> enter(loader);
diff --git a/ppapi/tests/arch_dependent_sizes_32.h b/ppapi/tests/arch_dependent_sizes_32.h
index f797494..34b6d86 100644
--- a/ppapi/tests/arch_dependent_sizes_32.h
+++ b/ppapi/tests/arch_dependent_sizes_32.h
@@ -15,7 +15,7 @@ PP_COMPILE_ASSERT_SIZE_IN_BYTES(GLintptr, 4);
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(GLsizeiptr, 4);
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_CompletionCallback_Func, 4);
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_URLLoaderTrusted_StatusCallback, 4);
-PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_CompletionCallback, 8);
+PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_CompletionCallback, 12);
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_FileChooserOptions_Dev, 8);
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_Picture_Dev, 24);
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_VideoBitstreamBuffer_Dev, 12);
diff --git a/ppapi/tests/arch_dependent_sizes_64.h b/ppapi/tests/arch_dependent_sizes_64.h
index 378c5b3..302938a 100644
--- a/ppapi/tests/arch_dependent_sizes_64.h
+++ b/ppapi/tests/arch_dependent_sizes_64.h
@@ -15,7 +15,7 @@ PP_COMPILE_ASSERT_SIZE_IN_BYTES(GLintptr, 8);
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(GLsizeiptr, 8);
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_CompletionCallback_Func, 8);
 PP_COMPILE_ASSERT_SIZE_IN_BYTES(PP_URLLoaderTrusted_StatusCallback, 8);
-PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_CompletionCallback, 16);
+PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_CompletionCallback, 24);
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_FileChooserOptions_Dev, 16);
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_Picture_Dev, 24);
 PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_VideoBitstreamBuffer_Dev, 12);
diff --git a/ppapi/tests/test_case.cc b/ppapi/tests/test_case.cc
index ec9f088..1d91ef5 100644
--- a/ppapi/tests/test_case.cc
+++ b/ppapi/tests/test_case.cc
@@ -11,7 +11,8 @@
 
 TestCase::TestCase(TestingInstance* instance)
     : instance_(instance),
-      testing_interface_(NULL) {
+      testing_interface_(NULL),
+      force_async_(false) {
 }
 
 TestCase::~TestCase() {
diff --git a/ppapi/tests/test_case.h b/ppapi/tests/test_case.h
index 5e77d0d..5ec4435 100644
--- a/ppapi/tests/test_case.h
+++ b/ppapi/tests/test_case.h
@@ -69,6 +69,9 @@ class TestCase {
   // NULL unless InitTestingInterface is called.
   const PPB_Testing_Dev* testing_interface_;
 
+  // Force asynchronous completion of any operation taking a callback.
+  bool force_async_;
+
  private:
   // Holds the test object, if any was retrieved from CreateTestObject.
   pp::Var test_object_;
@@ -114,10 +117,22 @@ class TestCaseFactory {
 
 // Helper macro for calling functions implementing specific tests in the
 // RunTest function. This assumes the function name is TestFoo where Foo is the
-// test name,
+// test |name|.
 #define RUN_TEST(name) \
+  force_async_ = false; \
   instance_->LogTest(#name, Test##name());
 
+// Like RUN_TEST above but forces functions taking callbacks to complete
+// asynchronously on success or error.
+#define RUN_TEST_FORCEASYNC(name) \
+  force_async_ = true; \
+  instance_->LogTest(#name"ForceAsync", Test##name());
+
+#define RUN_TEST_FORCEASYNC_AND_NOT(name) \
+  RUN_TEST_FORCEASYNC(name); \
+  RUN_TEST(name);
+
+
 // Helper macros for checking values in tests, and returning a location
 // description of the test fails.
 #define ASSERT_TRUE(cmd) \
diff --git a/ppapi/tests/test_directory_reader.cc b/ppapi/tests/test_directory_reader.cc
index 91996f3..874abcb 100644
--- a/ppapi/tests/test_directory_reader.cc
+++ b/ppapi/tests/test_directory_reader.cc
@@ -80,10 +80,12 @@ void TestDirectoryReader::RunTest() {
 }
 
 std::string TestDirectoryReader::TestGetNextFile() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   pp::FileSystem_Dev file_system(
       instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -100,6 +102,8 @@ std::string TestDirectoryReader::TestGetNextFile() {
     return ReportError("DeleteDirectoryRecursively", rv);
 
   rv = test_dir.MakeDirectory(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -113,6 +117,8 @@ std::string TestDirectoryReader::TestGetNextFile() {
 
     pp::FileIO_Dev file_io(instance_);
     rv = file_io.Open(file_ref, PP_FILEOPENFLAG_CREATE, callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Open force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -128,6 +134,8 @@ std::string TestDirectoryReader::TestGetNextFile() {
     pp::FileRef_Dev file_ref(file_system, buffer);
 
     rv = file_ref.MakeDirectory(callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileRef::MakeDirectory force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -144,6 +152,8 @@ std::string TestDirectoryReader::TestGetNextFile() {
     pp::DirectoryEntry_Dev entry;
     do {
       rv = directory_reader.GetNextEntry(&entry, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("DirectoryReader::GetNextEntry force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -188,6 +198,8 @@ std::string TestDirectoryReader::TestGetNextFile() {
     callback.reset_run_count();
     // Note that the directory reader will be deleted immediately.
     rv = pp::DirectoryReader_Dev(test_dir).GetNextEntry(&entry, callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("DirectoryReader::GetNextEntry force_async", rv);
     if (callback.run_count() > 0)
       return "DirectoryReader::GetNextEntry ran callback synchronously.";
 
diff --git a/ppapi/tests/test_file_io.cc b/ppapi/tests/test_file_io.cc
index 423016a..c6c2d63 100644
--- a/ppapi/tests/test_file_io.cc
+++ b/ppapi/tests/test_file_io.cc
@@ -111,21 +111,25 @@ bool TestFileIO::Init() {
 }
 
 void TestFileIO::RunTest() {
-  RUN_TEST(Open);
-  RUN_TEST(ReadWriteSetLength);
-  RUN_TEST(TouchQuery);
-  RUN_TEST(AbortCalls);
+  RUN_TEST_FORCEASYNC_AND_NOT(Open);
+  RUN_TEST_FORCEASYNC_AND_NOT(ReadWriteSetLength);
+  RUN_TEST_FORCEASYNC_AND_NOT(TouchQuery);
+  RUN_TEST_FORCEASYNC_AND_NOT(TouchQuery);
+  RUN_TEST_FORCEASYNC_AND_NOT(AbortCalls);
+  RUN_TEST_FORCEASYNC_AND_NOT(AbortCalls);
   // TODO(viettrungluu): add tests:
   //  - that PP_ERROR_PENDING is correctly returned
   //  - that operations respect the file open modes (flags)
 }
 
 std::string TestFileIO::TestOpen() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   pp::FileRef_Dev file_ref(file_system, "/file_open");
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -217,11 +221,13 @@ std::string TestFileIO::TestOpen() {
 }
 
 std::string TestFileIO::TestReadWriteSetLength() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   pp::FileRef_Dev file_ref(file_system, "/file_read_write_setlength");
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -234,6 +240,8 @@ std::string TestFileIO::TestReadWriteSetLength() {
                     PP_FILEOPENFLAG_READ |
                     PP_FILEOPENFLAG_WRITE,
                     callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -254,6 +262,8 @@ std::string TestFileIO::TestReadWriteSetLength() {
 
   // Truncate the file.
   rv = file_io.SetLength(4, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::SetLength force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -291,6 +301,8 @@ std::string TestFileIO::TestReadWriteSetLength() {
 
   // Extend the file.
   rv = file_io.SetLength(16, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::SetLength force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -332,10 +344,12 @@ std::string TestFileIO::TestReadWriteSetLength() {
 }
 
 std::string TestFileIO::TestTouchQuery() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -348,6 +362,8 @@ std::string TestFileIO::TestTouchQuery() {
                     PP_FILEOPENFLAG_TRUNCATE |
                     PP_FILEOPENFLAG_WRITE,
                     callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -355,6 +371,8 @@ std::string TestFileIO::TestTouchQuery() {
 
   // Write some data to have a non-zero file size.
   rv = file_io.Write(0, "test", 4, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Write force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != 4)
@@ -365,41 +383,49 @@ std::string TestFileIO::TestTouchQuery() {
   const PP_Time last_access_time = 123 * 24 * 3600.0;
   const PP_Time last_modified_time = 246.0;
   rv = file_io.Touch(last_access_time, last_modified_time, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Touch force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Touch", rv);
+    return ReportError("FileIO::Touch", rv);
 
   PP_FileInfo_Dev info;
   rv = file_io.Query(&info, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Query force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Query", rv);
+    return ReportError("FileIO::Query", rv);
 
   if ((info.size != 4) ||
       (info.type != PP_FILETYPE_REGULAR) ||
       (info.system_type != PP_FILESYSTEMTYPE_LOCALTEMPORARY) ||
       (info.last_access_time != last_access_time) ||
       (info.last_modified_time != last_modified_time))
-    return "FileSystem::Query() has returned bad data.";
+    return "FileIO::Query() has returned bad data.";
 
   // Call |Query()| again, to make sure it works a second time.
   rv = file_io.Query(&info, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Query force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Query", rv);
+    return ReportError("FileIO::Query", rv);
 
   PASS();
 }
 
 std::string TestFileIO::TestAbortCalls() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   pp::FileRef_Dev file_ref(file_system, "/file_abort_calls");
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -411,6 +437,8 @@ std::string TestFileIO::TestAbortCalls() {
     rv = file_io.Open(file_ref,
                       PP_FILEOPENFLAG_CREATE | PP_FILEOPENFLAG_WRITE,
                       callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Open force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -430,6 +458,8 @@ std::string TestFileIO::TestAbortCalls() {
     callback.reset_run_count();
     rv = pp::FileIO_Dev(instance_)
         .Open(file_ref, PP_FILEOPENFLAG_READ,callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Open force_async", rv);
     if (callback.run_count() > 0)
       return "FileIO::Open ran callback synchronously.";
     if (rv == PP_OK_COMPLETIONPENDING) {
@@ -447,6 +477,8 @@ std::string TestFileIO::TestAbortCalls() {
     {
       pp::FileIO_Dev file_io(instance_);
       rv = file_io.Open(file_ref, PP_FILEOPENFLAG_READ, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -454,6 +486,8 @@ std::string TestFileIO::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = file_io.Query(&info, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Query force_async", rv);
     }  // Destroy |file_io|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       // Save a copy and make sure |info| doesn't get written to.
@@ -474,6 +508,8 @@ std::string TestFileIO::TestAbortCalls() {
     {
       pp::FileIO_Dev file_io(instance_);
       rv = file_io.Open(file_ref, PP_FILEOPENFLAG_WRITE, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -481,6 +517,8 @@ std::string TestFileIO::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = file_io.Touch(0, 0, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Touch force_async", rv);
     }  // Destroy |file_io|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       rv = callback.WaitForResult();
@@ -497,6 +535,8 @@ std::string TestFileIO::TestAbortCalls() {
     {
       pp::FileIO_Dev file_io(instance_);
       rv = file_io.Open(file_ref, PP_FILEOPENFLAG_READ, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -504,6 +544,8 @@ std::string TestFileIO::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = file_io.Read(0, buf, sizeof(buf), callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Read force_async", rv);
     }  // Destroy |file_io|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       // Save a copy and make sure |buf| doesn't get written to.
@@ -525,6 +567,8 @@ std::string TestFileIO::TestAbortCalls() {
     {
       pp::FileIO_Dev file_io(instance_);
       rv = file_io.Open(file_ref, PP_FILEOPENFLAG_READ, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -532,6 +576,8 @@ std::string TestFileIO::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = file_io.Write(0, buf, sizeof(buf), callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Write force_async", rv);
     }  // Destroy |file_io|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       rv = callback.WaitForResult();
@@ -547,6 +593,8 @@ std::string TestFileIO::TestAbortCalls() {
     {
       pp::FileIO_Dev file_io(instance_);
       rv = file_io.Open(file_ref, PP_FILEOPENFLAG_READ, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -554,6 +602,8 @@ std::string TestFileIO::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = file_io.SetLength(3, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::SetLength force_async", rv);
     }  // Destroy |file_io|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       rv = callback.WaitForResult();
@@ -569,6 +619,8 @@ std::string TestFileIO::TestAbortCalls() {
     {
       pp::FileIO_Dev file_io(instance_);
       rv = file_io.Open(file_ref, PP_FILEOPENFLAG_READ, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -576,6 +628,8 @@ std::string TestFileIO::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = file_io.Flush(callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("FileIO::Flush force_async", rv);
     }  // Destroy |file_io|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       rv = callback.WaitForResult();
@@ -614,7 +668,7 @@ std::string TestFileIO::MatchOpenExpectations(pp::FileSystem_Dev* file_system,
   bool open_if_exists = !!(expectations & OPEN_IF_EXISTS);
   bool truncate_if_exists = !!(expectations & TRUNCATE_IF_EXISTS);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   pp::FileRef_Dev existent_file_ref(
       *file_system, "/match_open_expectation_existent_non_empty_file");
   pp::FileRef_Dev nonexistent_file_ref(
@@ -623,12 +677,16 @@ std::string TestFileIO::MatchOpenExpectations(pp::FileSystem_Dev* file_system,
   // Setup files for test.
   {
     int32_t rv = existent_file_ref.Delete(callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileRef::Delete force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK && rv != PP_ERROR_FILENOTFOUND)
       return ReportError("FileRef::Delete", rv);
 
     rv = nonexistent_file_ref.Delete(callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileRef::Delete force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK && rv != PP_ERROR_FILENOTFOUND)
@@ -638,6 +696,8 @@ std::string TestFileIO::MatchOpenExpectations(pp::FileSystem_Dev* file_system,
     rv = existent_file_io.Open(existent_file_ref,
                                PP_FILEOPENFLAG_CREATE | PP_FILEOPENFLAG_WRITE,
                                callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Open force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -651,6 +711,8 @@ std::string TestFileIO::MatchOpenExpectations(pp::FileSystem_Dev* file_system,
 
   pp::FileIO_Dev existent_file_io(instance_);
   int32_t rv = existent_file_io.Open(existent_file_ref, open_flags, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if ((invalid_combination && rv == PP_OK) ||
@@ -661,6 +723,8 @@ std::string TestFileIO::MatchOpenExpectations(pp::FileSystem_Dev* file_system,
   if (!invalid_combination && open_if_exists) {
     PP_FileInfo_Dev info;
     rv = existent_file_io.Query(&info, callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Query force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -672,6 +736,8 @@ std::string TestFileIO::MatchOpenExpectations(pp::FileSystem_Dev* file_system,
 
   pp::FileIO_Dev nonexistent_file_io(instance_);
   rv = nonexistent_file_io.Open(nonexistent_file_ref, open_flags, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if ((invalid_combination && rv == PP_OK) ||
diff --git a/ppapi/tests/test_file_ref.cc b/ppapi/tests/test_file_ref.cc
index 2fa8e5b..7ca032f 100644
--- a/ppapi/tests/test_file_ref.cc
+++ b/ppapi/tests/test_file_ref.cc
@@ -44,14 +44,14 @@ bool TestFileRef::Init() {
 }
 
 void TestFileRef::RunTest() {
-  RUN_TEST(GetFileSystemType);
-  RUN_TEST(GetName);
-  RUN_TEST(GetPath);
-  RUN_TEST(GetParent);
-  RUN_TEST(MakeDirectory);
-  RUN_TEST(QueryAndTouchFile);
-  RUN_TEST(DeleteFileAndDirectory);
-  RUN_TEST(RenameFileAndDirectory);
+  RUN_TEST_FORCEASYNC_AND_NOT(GetFileSystemType);
+  RUN_TEST_FORCEASYNC_AND_NOT(GetName);
+  RUN_TEST_FORCEASYNC_AND_NOT(GetPath);
+  RUN_TEST_FORCEASYNC_AND_NOT(GetParent);
+  RUN_TEST_FORCEASYNC_AND_NOT(MakeDirectory);
+  RUN_TEST_FORCEASYNC_AND_NOT(QueryAndTouchFile);
+  RUN_TEST_FORCEASYNC_AND_NOT(DeleteFileAndDirectory);
+  RUN_TEST_FORCEASYNC_AND_NOT(RenameFileAndDirectory);
 }
 
 std::string TestFileRef::TestGetFileSystemType() {
@@ -72,10 +72,12 @@ std::string TestFileRef::TestGetFileSystemType() {
   request.SetURL("test_url_loader_data/hello.txt");
   request.SetStreamToFile(true);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -121,10 +123,12 @@ std::string TestFileRef::TestGetName() {
   request.SetURL("test_url_loader_data/hello.txt");
   request.SetStreamToFile(true);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -165,10 +169,12 @@ std::string TestFileRef::TestGetPath() {
   request.SetURL("test_url_loader_data/hello.txt");
   request.SetStreamToFile(true);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -220,10 +226,12 @@ std::string TestFileRef::TestGetParent() {
   request.SetURL("test_url_loader_data/hello.txt");
   request.SetStreamToFile(true);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -244,11 +252,13 @@ std::string TestFileRef::TestGetParent() {
 }
 
 std::string TestFileRef::TestMakeDirectory() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   // Open.
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -257,6 +267,8 @@ std::string TestFileRef::TestMakeDirectory() {
   // MakeDirectory.
   pp::FileRef_Dev dir_ref(file_system, "/test_dir_make_directory");
   rv = dir_ref.MakeDirectory(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -268,6 +280,8 @@ std::string TestFileRef::TestMakeDirectory() {
       .MakeDirectory(callback);
   if (callback.run_count() > 0)
     return "FileSystem::MakeDirectory ran callback synchronously.";
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
@@ -279,6 +293,8 @@ std::string TestFileRef::TestMakeDirectory() {
   // MakeDirectoryIncludingAncestors.
   dir_ref = pp::FileRef_Dev(file_system, "/dir_make_dir_1/dir_make_dir_2");
   rv = dir_ref.MakeDirectoryIncludingAncestors(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -292,6 +308,9 @@ std::string TestFileRef::TestMakeDirectory() {
     return "FileSystem::MakeDirectoryIncludingAncestors "
            "ran callback synchronously.";
   }
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError(
+        "FileSystem::MakeDirectoryIncludingAncestors force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
@@ -303,6 +322,8 @@ std::string TestFileRef::TestMakeDirectory() {
   // MakeDirectory with nested path.
   dir_ref = pp::FileRef_Dev(file_system, "/dir_make_dir_3/dir_make_dir_4");
   rv = dir_ref.MakeDirectory(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv == PP_OK) {
@@ -314,9 +335,11 @@ std::string TestFileRef::TestMakeDirectory() {
 }
 
 std::string TestFileRef::TestQueryAndTouchFile() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -329,6 +352,8 @@ std::string TestFileRef::TestQueryAndTouchFile() {
                     PP_FILEOPENFLAG_TRUNCATE |
                     PP_FILEOPENFLAG_WRITE,
                     callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -336,6 +361,8 @@ std::string TestFileRef::TestQueryAndTouchFile() {
 
   // Write some data to have a non-zero file size.
   rv = file_io.Write(0, "test", 4, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Write force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != 4)
@@ -347,6 +374,8 @@ std::string TestFileRef::TestQueryAndTouchFile() {
   const PP_Time last_access_time = 123 * 24 * 3600.0;
   const PP_Time last_modified_time = 246.0;
   rv = file_ref.Touch(last_access_time, last_modified_time, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Touch force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -358,6 +387,8 @@ std::string TestFileRef::TestQueryAndTouchFile() {
       .Touch(last_access_time, last_modified_time, callback);
   if (callback.run_count() > 0)
     return "FileSystem::Touch ran callback synchronously.";
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Touch force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
@@ -369,6 +400,8 @@ std::string TestFileRef::TestQueryAndTouchFile() {
   // Query.
   PP_FileInfo_Dev info;
   rv = file_io.Query(&info, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Query force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -389,6 +422,8 @@ std::string TestFileRef::TestQueryAndTouchFile() {
       last_access_time, last_modified_time, callback);
   if (callback.run_count() > 0)
     return "FileSystem::Touch ran callback synchronously.";
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Touch force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
@@ -401,9 +436,11 @@ std::string TestFileRef::TestQueryAndTouchFile() {
 }
 
 std::string TestFileRef::TestDeleteFileAndDirectory() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -412,57 +449,73 @@ std::string TestFileRef::TestDeleteFileAndDirectory() {
   pp::FileRef_Dev file_ref(file_system, "/file_delete");
   pp::FileIO_Dev file_io(instance_);
   rv = file_io.Open(file_ref, PP_FILEOPENFLAG_CREATE, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
     return ReportError("FileIO::Open", rv);
 
   rv = file_ref.Delete(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Delete force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Delete", rv);
+    return ReportError("FileRef::Delete", rv);
 
   pp::FileRef_Dev dir_ref(file_system, "/dir_delete");
   rv = dir_ref.MakeDirectory(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::MakeDirectory", rv);
+    return ReportError("FileRef::MakeDirectory", rv);
 
   rv = dir_ref.Delete(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Delete", rv);
+    return ReportError("FileRef::Delete", rv);
 
   pp::FileRef_Dev nested_dir_ref(file_system, "/dir_delete_1/dir_delete_2");
   rv = nested_dir_ref.MakeDirectoryIncludingAncestors(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::MakeDirectoryIncludingAncestors", rv);
+    return ReportError("FileRef::MakeDirectoryIncludingAncestors", rv);
 
   // Hang on to a ref to the parent; otherwise the callback will be aborted.
   pp::FileRef_Dev parent_dir_ref = nested_dir_ref.GetParent();
   rv = parent_dir_ref.Delete(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_ERROR_FAILED)
-    return ReportError("FileSystem::Delete", rv);
+    return ReportError("FileRef::Delete", rv);
 
   pp::FileRef_Dev nonexistent_file_ref(file_system, "/nonexistent_file_delete");
   rv = nonexistent_file_ref.Delete(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_ERROR_FILENOTFOUND)
-    return ReportError("FileSystem::Delete", rv);
+    return ReportError("FileRef::Delete", rv);
 
   // Delete aborted.
   {
     pp::FileRef_Dev file_ref_abort(file_system, "/file_delete_abort");
     pp::FileIO_Dev file_io_abort(instance_);
     rv = file_io_abort.Open(file_ref_abort, PP_FILEOPENFLAG_CREATE, callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Open force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -472,22 +525,26 @@ std::string TestFileRef::TestDeleteFileAndDirectory() {
     rv = file_ref_abort.Delete(callback);
   }
   if (callback.run_count() > 0)
-    return "FileSystem::Delete ran callback synchronously.";
+    return "FileRef::Delete ran callback synchronously.";
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
-      return "FileSystem::Delete not aborted.";
+      return "FileRef::Delete not aborted.";
   } else if (rv != PP_OK) {
-    return ReportError("FileSystem::Delete", rv);
+    return ReportError("FileRef::Delete", rv);
   }
 
   PASS();
 }
 
 std::string TestFileRef::TestRenameFileAndDirectory() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv = file_system.Open(1024, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -496,6 +553,8 @@ std::string TestFileRef::TestRenameFileAndDirectory() {
   pp::FileRef_Dev file_ref(file_system, "/file_rename");
   pp::FileIO_Dev file_io(instance_);
   rv = file_io.Open(file_ref, PP_FILEOPENFLAG_CREATE, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -503,38 +562,48 @@ std::string TestFileRef::TestRenameFileAndDirectory() {
 
   pp::FileRef_Dev target_file_ref(file_system, "/target_file_rename");
   rv = file_ref.Rename(target_file_ref, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Rename force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Rename", rv);
+    return ReportError("FileRef::Rename", rv);
 
   pp::FileRef_Dev dir_ref(file_system, "/dir_rename");
   rv = dir_ref.MakeDirectory(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::MakeDirectory", rv);
+    return ReportError("FileRef::MakeDirectory", rv);
 
   pp::FileRef_Dev target_dir_ref(file_system, "/target_dir_rename");
   rv = dir_ref.Rename(target_dir_ref, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Rename force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::Rename", rv);
+    return ReportError("FileRef::Rename", rv);
 
   pp::FileRef_Dev nested_dir_ref(file_system, "/dir_rename_1/dir_rename_2");
   rv = nested_dir_ref.MakeDirectoryIncludingAncestors(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::MakeDirectory force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
-    return ReportError("FileSystem::MakeDirectoryIncludingAncestors", rv);
+    return ReportError("FileRef::MakeDirectoryIncludingAncestors", rv);
 
   pp::FileRef_Dev target_nested_dir_ref(file_system, "/dir_rename_1");
   rv = nested_dir_ref.Rename(target_nested_dir_ref, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileRef::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_ERROR_FAILED)
-    return ReportError("FileSystem::Rename", rv);
+    return ReportError("FileRef::Rename", rv);
 
   // Rename aborted.
   // TODO(viettrungluu): Figure out what we want to do if the target file
@@ -545,6 +614,8 @@ std::string TestFileRef::TestRenameFileAndDirectory() {
     pp::FileRef_Dev file_ref_abort(file_system, "/file_rename_abort");
     pp::FileIO_Dev file_io_abort(instance_);
     rv = file_io_abort.Open(file_ref_abort, PP_FILEOPENFLAG_CREATE, callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Open force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv != PP_OK)
@@ -555,6 +626,8 @@ std::string TestFileRef::TestRenameFileAndDirectory() {
   }
   if (callback.run_count() > 0)
     return "FileSystem::Rename ran callback synchronously.";
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Rename force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
diff --git a/ppapi/tests/test_file_system.cc b/ppapi/tests/test_file_system.cc
index 7758f5f..fe5c902 100644
--- a/ppapi/tests/test_file_system.cc
+++ b/ppapi/tests/test_file_system.cc
@@ -18,12 +18,12 @@ bool TestFileSystem::Init() {
 }
 
 void TestFileSystem::RunTest() {
-  RUN_TEST(Open);
-  RUN_TEST(MultipleOpens);
+  RUN_TEST_FORCEASYNC_AND_NOT(Open);
+  RUN_TEST_FORCEASYNC_AND_NOT(MultipleOpens);
 }
 
 std::string TestFileSystem::TestOpen() {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   // Open.
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
@@ -39,6 +39,8 @@ std::string TestFileSystem::TestOpen() {
       .Open(1024, callback);
   if (callback.run_count() > 0)
     return "FileSystem::Open ran callback synchronously.";
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING) {
     rv = callback.WaitForResult();
     if (rv != PP_ERROR_ABORTED)
@@ -53,27 +55,32 @@ std::string TestFileSystem::TestOpen() {
 std::string TestFileSystem::TestMultipleOpens() {
   // Should not allow multiple opens, no matter the first open has completed or
   // not.
-  TestCompletionCallback callback_1(instance_->pp_instance());
+  TestCompletionCallback callback_1(instance_->pp_instance(), force_async_);
   pp::FileSystem_Dev file_system(instance_, PP_FILESYSTEMTYPE_LOCALTEMPORARY);
   int32_t rv_1 = file_system.Open(1024, callback_1);
   if (callback_1.run_count() > 0)
-    return "FileSystem::Open ran callback synchronously.";
+    return "FileSystem::Open1 ran callback synchronously.";
+  if (force_async_ && rv_1 != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open1 force_async", rv_1);
 
-  TestCompletionCallback callback_2(instance_->pp_instance());
+  TestCompletionCallback callback_2(instance_->pp_instance(), force_async_);
   int32_t rv_2 = file_system.Open(1024, callback_2);
+  if (force_async_ && rv_2 != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open2 force_async", rv_2);
   if (rv_2 == PP_OK_COMPLETIONPENDING || rv_2 == PP_OK)
-    return "FileSystem::Open should not allow multiple opens.";
+    return "FileSystem::Open2 should not allow multiple opens.";
 
   if (rv_1 == PP_OK_COMPLETIONPENDING)
     rv_1 = callback_1.WaitForResult();
   if (rv_1 != PP_OK)
-    return ReportError("FileSystem::Open", rv_1);
+    return ReportError("FileSystem::Open1", rv_1);
 
-  TestCompletionCallback callback_3(instance_->pp_instance());
+  TestCompletionCallback callback_3(instance_->pp_instance(), force_async_);
   int32_t rv_3 = file_system.Open(1024, callback_3);
+  if (force_async_ && rv_3 != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileSystem::Open3 force_async", rv_3);
   if (rv_3 == PP_OK_COMPLETIONPENDING || rv_3 == PP_OK)
-    return "FileSystem::Open should not allow multiple opens.";
+    return "FileSystem::Open3 should not allow multiple opens.";
 
   PASS();
 }
-
diff --git a/ppapi/tests/test_graphics_2d.cc b/ppapi/tests/test_graphics_2d.cc
index 28483b4..2917180 100644
--- a/ppapi/tests/test_graphics_2d.cc
+++ b/ppapi/tests/test_graphics_2d.cc
@@ -43,15 +43,15 @@ bool TestGraphics2D::Init() {
 }
 
 void TestGraphics2D::RunTest() {
-  instance_->LogTest("InvalidResource", TestInvalidResource());
-  instance_->LogTest("InvalidSize", TestInvalidSize());
-  instance_->LogTest("Humongous", TestHumongous());
-  instance_->LogTest("InitToZero", TestInitToZero());
-  instance_->LogTest("Describe", TestDescribe());
-  instance_->LogTest("Paint", TestPaint());
-  //instance_->LogTest("Scroll", TestScroll());  // TODO(brettw) implement.
-  instance_->LogTest("Replace", TestReplace());
-  instance_->LogTest("Flush", TestFlush());
+  RUN_TEST(InvalidResource);
+  RUN_TEST(InvalidSize);
+  RUN_TEST(Humongous);
+  RUN_TEST(InitToZero);
+  RUN_TEST(Describe);
+  RUN_TEST_FORCEASYNC_AND_NOT(Paint);
+  // RUN_TEST_FORCEASYNC_AND_NOT(Scroll);  // TODO(brettw) implement.
+  RUN_TEST_FORCEASYNC_AND_NOT(Replace);
+  RUN_TEST_FORCEASYNC_AND_NOT(Flush);
 }
 
 void TestGraphics2D::QuitMessageLoop() {
@@ -79,8 +79,11 @@ bool TestGraphics2D::IsDCUniformColor(const pp::Graphics2D& dc,
 }
 
 bool TestGraphics2D::FlushAndWaitForDone(pp::Graphics2D* context) {
-  pp::CompletionCallback cc(&FlushCallbackQuitMessageLoop, this);
+  int32_t flags = (force_async_ ? 0 : PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+  pp::CompletionCallback cc(&FlushCallbackQuitMessageLoop, this, flags);
   int32_t rv = context->Flush(cc);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return false;
   if (rv == PP_OK)
     return true;
   if (rv != PP_OK_COMPLETIONPENDING)
@@ -209,11 +212,11 @@ std::string TestGraphics2D::TestInvalidResource() {
   // Flush.
   if (graphics_2d_interface_->Flush(
           image.pp_resource(),
-          PP_MakeCompletionCallback(&FlushCallbackNOP, NULL)) == PP_OK)
+          PP_MakeOptionalCompletionCallback(&FlushCallbackNOP, NULL)) == PP_OK)
     return "Flush succeeded with a different resource";
   if (graphics_2d_interface_->Flush(
           null_context.pp_resource(),
-          PP_MakeCompletionCallback(&FlushCallbackNOP, NULL)) == PP_OK)
+          PP_MakeOptionalCompletionCallback(&FlushCallbackNOP, NULL)) == PP_OK)
     return "Flush succeeded with a NULL resource";
 
   // ReadImageData.
@@ -526,16 +529,27 @@ std::string TestGraphics2D::TestFlush() {
   if (!FlushAndWaitForDone(&dc_nopaints))
     return "Couldn't flush the nopaint device";
 
+  int32_t flags = (force_async_ ? 0 : PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
+
   // Test that multiple flushes fail if we don't get a callback in between.
-  rv = dc_nopaints.Flush(pp::CompletionCallback(&FlushCallbackNOP, NULL));
+  rv = dc_nopaints.Flush(pp::CompletionCallback(&FlushCallbackNOP, NULL,
+                                                flags));
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return "Flush must complete asynchronously.";
   if (rv != PP_OK && rv != PP_OK_COMPLETIONPENDING)
     return "Couldn't flush first time for multiple flush test.";
 
-  if (rv != PP_OK) {
-    // If the first flush would block, then a second should fail.
-    rv = dc_nopaints.Flush(pp::CompletionCallback(&FlushCallbackNOP, NULL));
-    if (rv == PP_OK || rv == PP_OK_COMPLETIONPENDING)
-      return "Second flush succeeded before callback ran.";
+  if (rv == PP_OK_COMPLETIONPENDING) {
+    // If the first flush completes asynchronously, then a second should fail.
+    rv = dc_nopaints.Flush(pp::CompletionCallback(&FlushCallbackNOP, NULL,
+                                                  flags));
+    if (force_async_) {
+      if (rv != PP_OK_COMPLETIONPENDING)
+        return "Second flush must fail asynchronously.";
+    } else {
+      if (rv == PP_OK || rv == PP_OK_COMPLETIONPENDING)
+        return "Second flush succeeded before callback ran.";
+    }
   }
 
   PASS();
diff --git a/ppapi/tests/test_transport.cc b/ppapi/tests/test_transport.cc
index fc41f17..d45112a 100644
--- a/ppapi/tests/test_transport.cc
+++ b/ppapi/tests/test_transport.cc
@@ -54,7 +54,7 @@ class StreamReader {
       buffer_.resize(kReadBufferSize);
       int result = transport_->Recv(
           &buffer_[0], buffer_.size(),
-          callback_factory_.NewCallback(&StreamReader::OnReadFinished));
+          callback_factory_.NewOptionalCallback(&StreamReader::OnReadFinished));
       if (result > 0)
         DidFinishRead(result);
       else
@@ -104,7 +104,7 @@ bool TestTransport::Init() {
 void TestTransport::RunTest() {
   RUN_TEST(Create);
   RUN_TEST(Connect);
-  RUN_TEST(SendDataUdp);
+  RUN_TEST_FORCEASYNC(SendDataUdp);
   RUN_TEST(SendDataTcp);
   RUN_TEST(ConnectAndCloseUdp);
   RUN_TEST(ConnectAndCloseTcp);
@@ -198,10 +198,15 @@ std::string TestTransport::TestSendDataUdp() {
     // Put packet index in the beginning.
     memcpy(&send_buffer[0], &i, sizeof(i));
 
-    TestCompletionCallback send_cb(instance_->pp_instance());
-    ASSERT_EQ(
-        transport2_->Send(&send_buffer[0], send_buffer.size(), send_cb),
-        static_cast<int>(send_buffer.size()));
+    TestCompletionCallback send_cb(instance_->pp_instance(), force_async_);
+    int32_t result = transport2_->Send(&send_buffer[0], send_buffer.size(),
+                                       send_cb);
+    if (force_async_) {
+      ASSERT_EQ(result, PP_OK_COMPLETIONPENDING);
+      ASSERT_EQ(send_cb.WaitForResult(), static_cast<int>(send_buffer.size()));
+    } else {
+      ASSERT_EQ(result, static_cast<int>(send_buffer.size()));
+    }
     sent_packets[i] = send_buffer;
   }
 
@@ -243,9 +248,11 @@ std::string TestTransport::TestSendDataTcp() {
 
   int pos = 0;
   while (pos < static_cast<int>(send_buffer.size())) {
-    TestCompletionCallback send_cb(instance_->pp_instance());
+    TestCompletionCallback send_cb(instance_->pp_instance(), force_async_);
     int result = transport2_->Send(
         &send_buffer[0] + pos, send_buffer.size() - pos, send_cb);
+    if (force_async_)
+      ASSERT_EQ(result, PP_OK_COMPLETIONPENDING);
     if (result == PP_OK_COMPLETIONPENDING)
       result = send_cb.WaitForResult();
     ASSERT_TRUE(result > 0);
diff --git a/ppapi/tests/test_url_loader.cc b/ppapi/tests/test_url_loader.cc
index 8fda286..6ecb15d 100644
--- a/ppapi/tests/test_url_loader.cc
+++ b/ppapi/tests/test_url_loader.cc
@@ -44,27 +44,29 @@ bool TestURLLoader::Init() {
 
 void TestURLLoader::RunTest() {
   RUN_TEST(BasicGET);
-  RUN_TEST(BasicPOST);
-  RUN_TEST(CompoundBodyPOST);
-  RUN_TEST(EmptyDataPOST);
+  RUN_TEST_FORCEASYNC(BasicPOST);
+  RUN_TEST_FORCEASYNC_AND_NOT(CompoundBodyPOST);
+  RUN_TEST_FORCEASYNC(EmptyDataPOST);
   RUN_TEST(BinaryDataPOST);
-  RUN_TEST(CustomRequestHeader);
-  RUN_TEST(IgnoresBogusContentLength);
+  RUN_TEST_FORCEASYNC_AND_NOT(CustomRequestHeader);
+  RUN_TEST_FORCEASYNC(IgnoresBogusContentLength);
   RUN_TEST(SameOriginRestriction);
-  RUN_TEST(CrossOriginRequest);
-  RUN_TEST(StreamToFile);
+  RUN_TEST_FORCEASYNC(CrossOriginRequest);
+  RUN_TEST_FORCEASYNC_AND_NOT(StreamToFile);
   RUN_TEST(AuditURLRedirect);
-  RUN_TEST(AbortCalls);
+  RUN_TEST_FORCEASYNC(AbortCalls);
 }
 
 std::string TestURLLoader::ReadEntireFile(pp::FileIO_Dev* file_io,
                                           std::string* data) {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   char buf[256];
   int64_t offset = 0;
 
   for (;;) {
     int32_t rv = file_io->Read(offset, buf, sizeof(buf), callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("FileIO::Read force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv < 0)
@@ -80,11 +82,13 @@ std::string TestURLLoader::ReadEntireFile(pp::FileIO_Dev* file_io,
 
 std::string TestURLLoader::ReadEntireResponseBody(pp::URLLoader* loader,
                                                   std::string* body) {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   char buf[2];  // Small so that multiple reads are needed.
 
   for (;;) {
     int32_t rv = loader->ReadResponseBody(buf, sizeof(buf), callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("URLLoader::ReadResponseBody force_async", rv);
     if (rv == PP_OK_COMPLETIONPENDING)
       rv = callback.WaitForResult();
     if (rv < 0)
@@ -100,10 +104,12 @@ std::string TestURLLoader::ReadEntireResponseBody(pp::URLLoader* loader,
 std::string TestURLLoader::LoadAndCompareBody(
     const pp::URLRequestInfo& request,
     const std::string& expected_body) {
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(*instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -197,10 +203,12 @@ std::string TestURLLoader::TestStreamToFile() {
   request.SetURL("test_url_loader_data/hello.txt");
   request.SetStreamToFile(true);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(*instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -218,6 +226,8 @@ std::string TestURLLoader::TestStreamToFile() {
     return "URLResponseInfo::GetBody returned null";
 
   rv = loader.FinishStreamingToFile(callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::FinishStreamingToFile force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -225,6 +235,8 @@ std::string TestURLLoader::TestStreamToFile() {
 
   pp::FileIO_Dev reader(instance_);
   rv = reader.Open(body, PP_FILEOPENFLAG_READ, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("FileIO::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -253,10 +265,12 @@ std::string TestURLLoader::TestSameOriginRestriction() {
   pp::URLRequestInfo request(instance_);
   request.SetURL("http://www.google.com/");
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(*instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
 
@@ -290,11 +304,13 @@ std::string TestURLLoader::TestCrossOriginRequest() {
   request.SetURL(cross_origin_url);
   request.SetAllowCrossOriginRequests(true);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(*instance_);
   int32_t rv = loader.Open(request, callback);
-  if (rv == PP_ERROR_WOULDBLOCK)
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
+  if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
 
   // We expect success since we allowed a cross-origin request.
@@ -312,10 +328,12 @@ std::string TestURLLoader::TestAuditURLRedirect() {
   request.SetURL("/server-redirect?www.google.com");
   request.SetFollowRedirects(false);
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
 
   pp::URLLoader loader(*instance_);
   int32_t rv = loader.Open(request, callback);
+  if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+    return ReportError("URLLoader::Open force_async", rv);
   if (rv == PP_OK_COMPLETIONPENDING)
     rv = callback.WaitForResult();
   if (rv != PP_OK)
@@ -339,13 +357,15 @@ std::string TestURLLoader::TestAbortCalls() {
   pp::URLRequestInfo request(instance_);
   request.SetURL("test_url_loader_data/hello.txt");
 
-  TestCompletionCallback callback(instance_->pp_instance());
+  TestCompletionCallback callback(instance_->pp_instance(), force_async_);
   int32_t rv;
 
   // Abort |Open()|.
   {
     callback.reset_run_count();
     rv = pp::URLLoader(*instance_).Open(request, callback);
+    if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+      return ReportError("URLLoader::Open force_async", rv);
     if (callback.run_count() > 0)
       return "URLLoader::Open ran callback synchronously.";
     if (rv == PP_OK_COMPLETIONPENDING) {
@@ -363,6 +383,8 @@ std::string TestURLLoader::TestAbortCalls() {
     {
       pp::URLLoader loader(*instance_);
       rv = loader.Open(request, callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("URLLoader::Open force_async", rv);
       if (rv == PP_OK_COMPLETIONPENDING)
         rv = callback.WaitForResult();
       if (rv != PP_OK)
@@ -370,6 +392,8 @@ std::string TestURLLoader::TestAbortCalls() {
 
       callback.reset_run_count();
       rv = loader.ReadResponseBody(buf, sizeof(buf), callback);
+      if (force_async_ && rv != PP_OK_COMPLETIONPENDING)
+        return ReportError("URLLoader::ReadResponseBody force_async", rv);
     }  // Destroy |loader|.
     if (rv == PP_OK_COMPLETIONPENDING) {
       // Save a copy and make sure |buf| doesn't get written to.
diff --git a/ppapi/tests/test_utils.cc b/ppapi/tests/test_utils.cc
index 01557ce..b51634bc 100644
--- a/ppapi/tests/test_utils.cc
+++ b/ppapi/tests/test_utils.cc
@@ -29,6 +29,17 @@ std::string ReportError(const char* method, int32_t error) {
 TestCompletionCallback::TestCompletionCallback(PP_Instance instance)
     : have_result_(false),
       result_(PP_OK_COMPLETIONPENDING),
+      force_async_(false),
+      post_quit_task_(false),
+      run_count_(0),
+      instance_(instance) {
+}
+
+TestCompletionCallback::TestCompletionCallback(PP_Instance instance,
+                                               bool force_async)
+    : have_result_(false),
+      result_(PP_OK_COMPLETIONPENDING),
+      force_async_(force_async),
       post_quit_task_(false),
       run_count_(0),
       instance_(instance) {
@@ -45,8 +56,10 @@ int32_t TestCompletionCallback::WaitForResult() {
 }
 
 TestCompletionCallback::operator pp::CompletionCallback() const {
+  int32_t flags = (force_async_ ? 0 : PP_COMPLETIONCALLBACK_FLAG_OPTIONAL);
   return pp::CompletionCallback(&TestCompletionCallback::Handler,
-                                const_cast<TestCompletionCallback*>(this));
+                                const_cast<TestCompletionCallback*>(this),
+                                flags);
 }
 
 // static
diff --git a/ppapi/tests/test_utils.h b/ppapi/tests/test_utils.h
index 721a048..e786aa8 100644
--- a/ppapi/tests/test_utils.h
+++ b/ppapi/tests/test_utils.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -18,6 +18,7 @@ std::string ReportError(const char* method, int32_t error);
 class TestCompletionCallback {
  public:
   TestCompletionCallback(PP_Instance instance);
+  TestCompletionCallback(PP_Instance instance, bool force_async);
 
   // Waits for the callback to be called and returns the
   // result. Returns immediately if the callback was previously called
@@ -38,6 +39,7 @@ class TestCompletionCallback {
 
   bool have_result_;
   int32_t result_;
+  bool force_async_;
   bool post_quit_task_;
   unsigned run_count_;
   PP_Instance instance_;
diff --git a/ppapi/thunk/common.cc b/ppapi/thunk/common.cc
new file mode 100644
index 0000000..b59f139
--- /dev/null
+++ b/ppapi/thunk/common.cc
@@ -0,0 +1,30 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ppapi/thunk/common.h"
+
+#include "base/message_loop.h"
+#include "ppapi/c/pp_errors.h"
+
+namespace ppapi {
+namespace thunk {
+
+int32_t MayForceCallback(PP_CompletionCallback callback, int32_t result) {
+  if (result == PP_OK_COMPLETIONPENDING)
+    return result;
+
+  if (callback.func == NULL ||
+      (callback.flags & PP_COMPLETIONCALLBACK_FLAG_OPTIONAL) != 0)
+    return result;
+
+  // TODO(polina): make this work off the main thread as well
+  // (At this point this should not be an issue because PPAPI is only supported
+  // on the main thread).
+  MessageLoop::current()->PostTask(FROM_HERE, NewRunnableFunction(
+      callback.func, callback.user_data, result));
+  return PP_OK_COMPLETIONPENDING;
+}
+
+}  // namespace thunk
+}  // namespace ppapi
diff --git a/ppapi/thunk/common.h b/ppapi/thunk/common.h
new file mode 100644
index 0000000..7966da4
--- /dev/null
+++ b/ppapi/thunk/common.h
@@ -0,0 +1,21 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PPAPI_THUNK_COMMON_H_
+#define PPAPI_THUNK_COMMON_H_
+
+#include "ppapi/c/pp_completion_callback.h"
+
+namespace ppapi {
+namespace thunk {
+
+// Skips callback invocation and returns |result| if callback function is NULL
+// or PP_COMPLETIONCALLBACK_FLAG_OPTIONAL is set. Otherwise, schedules the
+// callback with |result| as an argument and returns PP_OK_COMPLETIONPENDING.
+int32_t MayForceCallback(PP_CompletionCallback callback, int32_t result);
+
+}  // namespace thunk
+}  // namespace ppapi
+
+#endif  // PPAPI_THUNK_COMMON_H_
diff --git a/ppapi/thunk/ppb_audio_trusted_thunk.cc b/ppapi/thunk/ppb_audio_trusted_thunk.cc
index 5cb0bfd..05c1b4e 100644
--- a/ppapi/thunk/ppb_audio_trusted_thunk.cc
+++ b/ppapi/thunk/ppb_audio_trusted_thunk.cc
@@ -3,8 +3,9 @@
 // found in the LICENSE file.
 
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_audio_trusted_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -22,11 +23,12 @@ PP_Resource Create(PP_Instance instance_id) {
 
 int32_t Open(PP_Resource audio_id,
              PP_Resource config_id,
-             PP_CompletionCallback created) {
+             PP_CompletionCallback create_callback) {
   EnterResource<PPB_AudioTrusted_API> enter(audio_id, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->OpenTrusted(config_id, created);
+    return MayForceCallback(create_callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->OpenTrusted(config_id, create_callback);
+  return MayForceCallback(create_callback, result);
 }
 
 int32_t GetSyncSocket(PP_Resource audio_id, int* sync_socket) {
diff --git a/ppapi/thunk/ppb_broker_thunk.cc b/ppapi/thunk/ppb_broker_thunk.cc
index 1394ee9..1bfcea0 100644
--- a/ppapi/thunk/ppb_broker_thunk.cc
+++ b/ppapi/thunk/ppb_broker_thunk.cc
@@ -4,8 +4,9 @@
 
 #include "ppapi/c/trusted/ppb_broker_trusted.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_broker_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -30,8 +31,9 @@ int32_t Connect(PP_Resource resource,
                 PP_CompletionCallback connect_callback) {
   EnterResource<PPB_Broker_API> enter(resource, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Connect(connect_callback);
+    return MayForceCallback(connect_callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Connect(connect_callback);
+  return MayForceCallback(connect_callback, result);
 }
 
 int32_t GetHandle(PP_Resource resource, int32_t* handle) {
diff --git a/ppapi/thunk/ppb_directory_reader_thunk.cc b/ppapi/thunk/ppb_directory_reader_thunk.cc
index d1dfed4..c631194 100644
--- a/ppapi/thunk/ppb_directory_reader_thunk.cc
+++ b/ppapi/thunk/ppb_directory_reader_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/dev/ppb_directory_reader_dev.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_directory_reader_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -32,8 +33,9 @@ int32_t GetNextEntry(PP_Resource directory_reader,
                      PP_CompletionCallback callback) {
   EnterResource<PPB_DirectoryReader_API> enter(directory_reader, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->GetNextEntry(entry, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->GetNextEntry(entry, callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_DirectoryReader_Dev g_ppb_directory_reader_thunk = {
diff --git a/ppapi/thunk/ppb_file_chooser_thunk.cc b/ppapi/thunk/ppb_file_chooser_thunk.cc
index 8389725..224d248 100644
--- a/ppapi/thunk/ppb_file_chooser_thunk.cc
+++ b/ppapi/thunk/ppb_file_chooser_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/dev/ppb_file_chooser_dev.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_file_chooser_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -31,8 +32,9 @@ PP_Bool IsFileChooser(PP_Resource resource) {
 int32_t Show(PP_Resource chooser, PP_CompletionCallback callback) {
   EnterResource<PPB_FileChooser_API> enter(chooser, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Show(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Show(callback);
+  return MayForceCallback(callback, result);
 }
 
 PP_Resource GetNextChosenFile(PP_Resource chooser) {
diff --git a/ppapi/thunk/ppb_file_io_thunk.cc b/ppapi/thunk/ppb_file_io_thunk.cc
index 2aaaaa4..5c1f935 100644
--- a/ppapi/thunk/ppb_file_io_thunk.cc
+++ b/ppapi/thunk/ppb_file_io_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/dev/ppb_file_io_dev.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_file_io_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -33,8 +34,9 @@ int32_t Open(PP_Resource file_io,
              PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Open(file_ref, open_flags, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Open(file_ref, open_flags, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Query(PP_Resource file_io,
@@ -42,8 +44,9 @@ int32_t Query(PP_Resource file_io,
               PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Query(info, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Query(info, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Touch(PP_Resource file_io,
@@ -52,8 +55,10 @@ int32_t Touch(PP_Resource file_io,
               PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Touch(last_access_time, last_modified_time, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Touch(last_access_time, last_modified_time,
+                                         callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Read(PP_Resource file_io,
@@ -63,8 +68,10 @@ int32_t Read(PP_Resource file_io,
              PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Read(offset, buffer, bytes_to_read, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Read(offset, buffer, bytes_to_read,
+                                        callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Write(PP_Resource file_io,
@@ -74,8 +81,10 @@ int32_t Write(PP_Resource file_io,
               PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Write(offset, buffer, bytes_to_write, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Write(offset, buffer, bytes_to_write,
+                                         callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t SetLength(PP_Resource file_io,
@@ -83,16 +92,18 @@ int32_t SetLength(PP_Resource file_io,
                   PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->SetLength(length, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->SetLength(length, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Flush(PP_Resource file_io,
               PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Flush(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Flush(callback);
+  return MayForceCallback(callback, result);
 }
 
 void Close(PP_Resource file_io) {
diff --git a/ppapi/thunk/ppb_file_io_trusted_thunk.cc b/ppapi/thunk/ppb_file_io_trusted_thunk.cc
index 1cba025..38ad460 100644
--- a/ppapi/thunk/ppb_file_io_trusted_thunk.cc
+++ b/ppapi/thunk/ppb_file_io_trusted_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/dev/ppb_file_io_trusted_dev.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_file_io_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -28,8 +29,9 @@ int32_t WillWrite(PP_Resource file_io,
                   PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->WillWrite(offset, bytes_to_write, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result =  enter.object()->WillWrite(offset, bytes_to_write, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t WillSetLength(PP_Resource file_io,
@@ -37,8 +39,9 @@ int32_t WillSetLength(PP_Resource file_io,
                       PP_CompletionCallback callback) {
   EnterResource<PPB_FileIO_API> enter(file_io, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->WillSetLength(length, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->WillSetLength(length, callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_FileIOTrusted_Dev g_ppb_file_io_trusted_thunk = {
diff --git a/ppapi/thunk/ppb_file_ref_thunk.cc b/ppapi/thunk/ppb_file_ref_thunk.cc
index aeac135..af8de13 100644
--- a/ppapi/thunk/ppb_file_ref_thunk.cc
+++ b/ppapi/thunk/ppb_file_ref_thunk.cc
@@ -6,8 +6,9 @@
 #include "ppapi/c/dev/ppb_file_ref_dev.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_file_ref_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -61,8 +62,9 @@ int32_t MakeDirectory(PP_Resource directory_ref,
                       PP_CompletionCallback callback) {
   EnterResource<PPB_FileRef_API> enter(directory_ref, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->MakeDirectory(make_ancestors, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->MakeDirectory(make_ancestors, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Touch(PP_Resource file_ref,
@@ -71,16 +73,19 @@ int32_t Touch(PP_Resource file_ref,
               PP_CompletionCallback callback) {
   EnterResource<PPB_FileRef_API> enter(file_ref, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Touch(last_access_time, last_modified_time, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Touch(last_access_time, last_modified_time,
+                                         callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Delete(PP_Resource file_ref,
                PP_CompletionCallback callback) {
   EnterResource<PPB_FileRef_API> enter(file_ref, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Delete(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Delete(callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Rename(PP_Resource file_ref,
@@ -88,8 +93,9 @@ int32_t Rename(PP_Resource file_ref,
                PP_CompletionCallback callback) {
   EnterResource<PPB_FileRef_API> enter(file_ref, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Rename(new_file_ref, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Rename(new_file_ref, callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_FileRef_Dev g_ppb_file_ref_thunk = {
diff --git a/ppapi/thunk/ppb_file_system_thunk.cc b/ppapi/thunk/ppb_file_system_thunk.cc
index e1c4f6a..0d4099e 100644
--- a/ppapi/thunk/ppb_file_system_thunk.cc
+++ b/ppapi/thunk/ppb_file_system_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/dev/ppb_file_system_dev.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_file_system_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -32,8 +33,9 @@ int32_t Open(PP_Resource file_system,
              PP_CompletionCallback callback) {
   EnterResource<PPB_FileSystem_API> enter(file_system, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Open(expected_size, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Open(expected_size, callback);
+  return MayForceCallback(callback, result);
 }
 
 PP_FileSystemType_Dev GetType(PP_Resource file_system) {
diff --git a/ppapi/thunk/ppb_flash_menu_thunk.cc b/ppapi/thunk/ppb_flash_menu_thunk.cc
index f24ff72..3641e1e 100644
--- a/ppapi/thunk/ppb_flash_menu_thunk.cc
+++ b/ppapi/thunk/ppb_flash_menu_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/private/ppb_flash_menu.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_flash_menu_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -33,8 +34,9 @@ int32_t Show(PP_Resource resource,
              PP_CompletionCallback callback) {
   EnterResource<PPB_Flash_Menu_API> enter(resource, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Show(location, selected_id, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Show(location, selected_id, callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_Flash_Menu g_ppb_flash_menu_thunk = {
@@ -51,4 +53,3 @@ const PPB_Flash_Menu* GetPPB_Flash_Menu_Thunk() {
 
 }  // namespace thunk
 }  // namespace ppapi
-
diff --git a/ppapi/thunk/ppb_flash_net_connector_thunk.cc b/ppapi/thunk/ppb_flash_net_connector_thunk.cc
index e0bb05c..14cf751 100644
--- a/ppapi/thunk/ppb_flash_net_connector_thunk.cc
+++ b/ppapi/thunk/ppb_flash_net_connector_thunk.cc
@@ -5,8 +5,9 @@
 #include "ppapi/c/private/ppb_flash_net_connector.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_flash_net_connector_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -36,9 +37,11 @@ int32_t ConnectTcp(PP_Resource resource,
                    PP_CompletionCallback callback) {
   EnterResource<PPB_Flash_NetConnector_API> enter(resource, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->ConnectTcp(host, port, socket_out, local_addr_out,
-                                    remote_addr_out, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result =
+      enter.object()->ConnectTcp(host, port, socket_out, local_addr_out,
+                                 remote_addr_out, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t ConnectTcpAddress(PP_Resource resource,
@@ -49,9 +52,11 @@ int32_t ConnectTcpAddress(PP_Resource resource,
                           PP_CompletionCallback callback) {
   EnterResource<PPB_Flash_NetConnector_API> enter(resource, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->ConnectTcpAddress(addr, socket_out, local_addr_out,
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result =
+      enter.object()->ConnectTcpAddress(addr, socket_out, local_addr_out,
                                            remote_addr_out, callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_Flash_NetConnector g_ppb_flash_net_connector_thunk = {
@@ -69,4 +74,3 @@ const PPB_Flash_NetConnector* GetPPB_Flash_NetConnector_Thunk() {
 
 }  // namespace thunk
 }  // namespace ppapi
-
diff --git a/ppapi/thunk/ppb_graphics_2d_thunk.cc b/ppapi/thunk/ppb_graphics_2d_thunk.cc
index c26cac8..65aa4b0 100644
--- a/ppapi/thunk/ppb_graphics_2d_thunk.cc
+++ b/ppapi/thunk/ppb_graphics_2d_thunk.cc
@@ -5,6 +5,7 @@
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/ppb_graphics_2d.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
 #include "ppapi/thunk/ppb_graphics_2d_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
@@ -71,8 +72,9 @@ int32_t Flush(PP_Resource graphics_2d,
               PP_CompletionCallback callback) {
   EnterResource<PPB_Graphics2D_API> enter(graphics_2d, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Flush(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Flush(callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_Graphics2D g_ppb_graphics_2d_thunk = {
diff --git a/ppapi/thunk/ppb_graphics_3d_thunk.cc b/ppapi/thunk/ppb_graphics_3d_thunk.cc
index edac937..c3363f20 100644
--- a/ppapi/thunk/ppb_graphics_3d_thunk.cc
+++ b/ppapi/thunk/ppb_graphics_3d_thunk.cc
@@ -4,8 +4,9 @@
 
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_graphics_3d_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -66,8 +67,9 @@ int32_t SetAttribs(PP_Resource graphics_3d, int32_t* attrib_list) {
 int32_t SwapBuffers(PP_Resource graphics_3d, PP_CompletionCallback callback) {
   EnterGraphics3D enter(graphics_3d, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->SwapBuffers(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->SwapBuffers(callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_Graphics3D_Dev g_ppb_graphics_3d_thunk = {
diff --git a/ppapi/thunk/ppb_layer_compositor_thunk.cc b/ppapi/thunk/ppb_layer_compositor_thunk.cc
index 3e5cbef..783ad4d 100644
--- a/ppapi/thunk/ppb_layer_compositor_thunk.cc
+++ b/ppapi/thunk/ppb_layer_compositor_thunk.cc
@@ -4,8 +4,9 @@
 
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/dev/ppb_layer_compositor_dev.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_layer_compositor_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -45,7 +46,7 @@ void MarkAsDirty(PP_Resource compositor, PP_Resource layer) {
 
 int32_t SwapBuffers(PP_Resource compositor,
                     struct PP_CompletionCallback callback) {
-  return PP_ERROR_FAILED;
+  return MayForceCallback(callback, PP_ERROR_FAILED);
 }
 
 const PPB_LayerCompositor_Dev g_ppb_layer_compositor_thunk = {
diff --git a/ppapi/thunk/ppb_surface_3d_thunk.cc b/ppapi/thunk/ppb_surface_3d_thunk.cc
index 0c6d9e6..e7034cb 100644
--- a/ppapi/thunk/ppb_surface_3d_thunk.cc
+++ b/ppapi/thunk/ppb_surface_3d_thunk.cc
@@ -3,8 +3,9 @@
 // found in the LICENSE file.
 
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_surface_3d_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -47,8 +48,9 @@ int32_t SwapBuffers(PP_Resource surface,
                     PP_CompletionCallback callback) {
   EnterResource<PPB_Surface3D_API> enter(surface, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->SwapBuffers(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->SwapBuffers(callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_Surface3D_Dev g_ppb_surface_3d_thunk = {
diff --git a/ppapi/thunk/ppb_transport_thunk.cc b/ppapi/thunk/ppb_transport_thunk.cc
index 50ad4aa..cf573c5 100644
--- a/ppapi/thunk/ppb_transport_thunk.cc
+++ b/ppapi/thunk/ppb_transport_thunk.cc
@@ -4,8 +4,9 @@
 
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_transport_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -38,16 +39,18 @@ PP_Bool IsWritable(PP_Resource transport) {
 int32_t Connect(PP_Resource transport, PP_CompletionCallback callback) {
   EnterTransport enter(transport, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Connect(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Connect(callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t GetNextAddress(PP_Resource transport, PP_Var* address,
                        PP_CompletionCallback callback) {
   EnterTransport enter(transport, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->GetNextAddress(address, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->GetNextAddress(address, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t ReceiveRemoteAddress(PP_Resource transport, PP_Var address) {
@@ -61,16 +64,18 @@ int32_t Recv(PP_Resource transport, void* data, uint32_t len,
              PP_CompletionCallback callback) {
   EnterTransport enter(transport, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Recv(data, len, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Recv(data, len, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Send(PP_Resource transport, const void* data, uint32_t len,
              PP_CompletionCallback callback) {
   EnterTransport enter(transport, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Send(data, len, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Send(data, len, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Close(PP_Resource transport) {
diff --git a/ppapi/thunk/ppb_url_loader_thunk.cc b/ppapi/thunk/ppb_url_loader_thunk.cc
index e5c0b5a..236144f 100644
--- a/ppapi/thunk/ppb_url_loader_thunk.cc
+++ b/ppapi/thunk/ppb_url_loader_thunk.cc
@@ -4,8 +4,9 @@
 
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_url_loader_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -31,16 +32,18 @@ int32_t Open(PP_Resource loader,
              PP_CompletionCallback callback) {
   EnterResource<PPB_URLLoader_API> enter(loader, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Open(request_id, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Open(request_id, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t FollowRedirect(PP_Resource loader,
                        PP_CompletionCallback callback) {
   EnterResource<PPB_URLLoader_API> enter(loader, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->FollowRedirect(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->FollowRedirect(callback);
+  return MayForceCallback(callback, result);
 }
 
 PP_Bool GetUploadProgress(PP_Resource loader,
@@ -82,16 +85,19 @@ int32_t ReadResponseBody(PP_Resource loader,
                          PP_CompletionCallback callback) {
   EnterResource<PPB_URLLoader_API> enter(loader, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->ReadResponseBody(buffer, bytes_to_read, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->ReadResponseBody(buffer, bytes_to_read,
+                                                    callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t FinishStreamingToFile(PP_Resource loader,
                               PP_CompletionCallback callback) {
   EnterResource<PPB_URLLoader_API> enter(loader, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->FinishStreamingToFile(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->FinishStreamingToFile(callback);
+  return MayForceCallback(callback, result);
 }
 
 void Close(PP_Resource loader) {
diff --git a/ppapi/thunk/ppb_video_decoder_thunk.cc b/ppapi/thunk/ppb_video_decoder_thunk.cc
index f12a5b3..9d82113 100644
--- a/ppapi/thunk/ppb_video_decoder_thunk.cc
+++ b/ppapi/thunk/ppb_video_decoder_thunk.cc
@@ -3,8 +3,9 @@
 // found in the LICENSE file.
 
 #include "ppapi/c/pp_errors.h"
-#include "ppapi/thunk/thunk.h"
+#include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
+#include "ppapi/thunk/thunk.h"
 #include "ppapi/thunk/ppb_video_decoder_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
@@ -46,8 +47,10 @@ int32_t Initialize(PP_Resource video_decoder,
                    PP_CompletionCallback callback) {
   EnterVideoDecoder enter(video_decoder, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Initialize(context_id, decoder_config, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result =
+      enter.object()->Initialize(context_id, decoder_config, callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Decode(PP_Resource video_decoder,
@@ -55,8 +58,9 @@ int32_t Decode(PP_Resource video_decoder,
                PP_CompletionCallback callback) {
   EnterVideoDecoder enter(video_decoder, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Decode(bitstream_buffer, callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Decode(bitstream_buffer, callback);
+  return MayForceCallback(callback, result);
 }
 
 void AssignGLESBuffers(PP_Resource video_decoder,
@@ -84,16 +88,18 @@ void ReusePictureBuffer(PP_Resource video_decoder, int32_t picture_buffer_id) {
 int32_t Flush(PP_Resource video_decoder, PP_CompletionCallback callback) {
   EnterVideoDecoder enter(video_decoder, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Flush(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Flush(callback);
+  return MayForceCallback(callback, result);
 }
 
 int32_t Abort(PP_Resource video_decoder,
               PP_CompletionCallback callback) {
   EnterVideoDecoder enter(video_decoder, true);
   if (enter.failed())
-    return PP_ERROR_BADRESOURCE;
-  return enter.object()->Abort(callback);
+    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
+  int32_t result = enter.object()->Abort(callback);
+  return MayForceCallback(callback, result);
 }
 
 const PPB_VideoDecoder_Dev g_ppb_videodecoder_thunk = {
diff --git a/remoting/client/plugin/pepper_port_allocator_session.cc b/remoting/client/plugin/pepper_port_allocator_session.cc
index 8c5c598..ec7544e9 100644
--- a/remoting/client/plugin/pepper_port_allocator_session.cc
+++ b/remoting/client/plugin/pepper_port_allocator_session.cc
@@ -121,7 +121,7 @@ class PepperURLFetcher {
     fetch_callback_.reset(fetch_callback);
 
     pp::CompletionCallback callback =
-        callback_factory_.NewCallback(&PepperURLFetcher::DidOpen);
+        callback_factory_.NewOptionalCallback(&PepperURLFetcher::DidOpen);
     int rv = loader_.Open(request, callback);
     if (rv != PP_OK_COMPLETIONPENDING)
       callback.Run(rv);
@@ -130,7 +130,7 @@ class PepperURLFetcher {
  private:
   void ReadMore() {
     pp::CompletionCallback callback =
-        callback_factory_.NewCallback(&PepperURLFetcher::DidRead);
+        callback_factory_.NewOptionalCallback(&PepperURLFetcher::DidRead);
     int rv = loader_.ReadResponseBody(buf_, sizeof(buf_), callback);
     if (rv != PP_OK_COMPLETIONPENDING)
       callback.Run(rv);