Fix up some reference counting when WebPluginImpl::scriptableObject is called.

BUG= http://code.google.com/p/chromium-os/issues/detail?id=13605
TEST=none
Review URL: http://codereview.chromium.org/6731051

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@79712 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 35 insertions, 10 deletions

diff --git a/webkit/plugins/ppapi/message_channel.cc b/webkit/plugins/ppapi/message_channel.cc
index 684745a..b6f01d7 100644
--- a/webkit/plugins/ppapi/message_channel.cc
+++ b/webkit/plugins/ppapi/message_channel.cc
@@ -282,7 +282,8 @@ MessageChannel::MessageChannel(PluginInstance* instance)
       ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)) {
   VOID_TO_NPVARIANT(onmessage_invoker_);
 
-  // Now create an NPObject for receiving calls to postMessage.
+  // Now create an NPObject for receiving calls to postMessage. This sets the
+  // reference count to 1.  We release it in the destructor.
   NPObject* obj = WebBindings::createObject(NULL, &message_channel_class);
   DCHECK(obj);
   np_object_ = static_cast<MessageChannel::MessageChannelNPObject*>(obj);
@@ -381,9 +382,26 @@ void MessageChannel::PostMessageToNativeImpl(PP_Var message_data) {
 
 MessageChannel::~MessageChannel() {
   WebBindings::releaseObject(np_object_);
+  if (passthrough_object_)
+    WebBindings::releaseObject(passthrough_object_);
   WebBindings::releaseVariantValue(&onmessage_invoker_);
 }
 
+void MessageChannel::SetPassthroughObject(NPObject* passthrough) {
+  // Retain the passthrough object; We need to ensure it lives as long as this
+  // MessageChannel.
+  WebBindings::retainObject(passthrough);
+
+  // If we had a passthrough set already, release it. Note that we retain the
+  // incoming passthrough object first, so that we behave correctly if anyone
+  // invokes:
+  //   SetPassthroughObject(passthrough_object());
+  if (passthrough_object_)
+    WebBindings::releaseObject(passthrough_object_);
+
+  passthrough_object_ = passthrough;
+}
+
 }  // namespace ppapi
 }  // namespace webkit
 
diff --git a/webkit/plugins/ppapi/message_channel.h b/webkit/plugins/ppapi/message_channel.h
index c1a5456..efe4568 100644
--- a/webkit/plugins/ppapi/message_channel.h
+++ b/webkit/plugins/ppapi/message_channel.h
@@ -59,9 +59,7 @@ class MessageChannel {
   NPObject* passthrough_object() {
     return passthrough_object_;
   }
-  void set_passthrough_object(NPObject* passthrough) {
-    passthrough_object_ = passthrough;
-  }
+  void SetPassthroughObject(NPObject* passthrough);
 
   NPObject* np_object() { return np_object_; }
 
diff --git a/webkit/plugins/ppapi/plugin_object.cc b/webkit/plugins/ppapi/plugin_object.cc
index d99ef80..d5b9865 100644
--- a/webkit/plugins/ppapi/plugin_object.cc
+++ b/webkit/plugins/ppapi/plugin_object.cc
@@ -290,7 +290,14 @@ PP_Var PluginObject::Create(PluginInstance* instance,
   // We can just use a normal ObjectVar to refer to this object from the
   // plugin. It will hold a ref to the underlying NPObject which will in turn
   // hold our pluginObject.
-  return ObjectVar::NPObjectToPPVar(instance, wrapper);
+  PP_Var obj_var(ObjectVar::NPObjectToPPVar(instance, wrapper));
+
+  // Note that the ObjectVar constructor incremented the reference count, and so
+  // did WebBindings::createObject above. Now that the PP_Var has taken
+  // ownership, we need to release to balance out the createObject reference
+  // count bump.
+  WebBindings::releaseObject(wrapper);
+  return obj_var;
 }
 
 NPObject* PluginObject::GetNPObject() const {
diff --git a/webkit/plugins/ppapi/ppapi_webplugin_impl.cc b/webkit/plugins/ppapi/ppapi_webplugin_impl.cc
index 8e61354..8a35638 100644
--- a/webkit/plugins/ppapi/ppapi_webplugin_impl.cc
+++ b/webkit/plugins/ppapi/ppapi_webplugin_impl.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.
 
@@ -8,6 +8,7 @@
 
 #include "base/message_loop.h"
 #include "ppapi/c/pp_var.h"
+#include "third_party/WebKit/Source/WebKit/chromium/public/WebBindings.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebPluginParams.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebPoint.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebRect.h"
@@ -94,11 +95,12 @@ NPObject* WebPluginImpl::scriptableObject() {
   // If there's an InstanceObject, tell the Instance's MessageChannel to pass
   // any non-postMessage calls to it.
   if (object) {
-    instance_->message_channel().set_passthrough_object(
-        object->np_object());
+    instance_->message_channel().SetPassthroughObject(object->np_object());
   }
-  // And return the instance's MessageChannel.
-  return instance_->message_channel().np_object();
+  NPObject* message_channel_np_object(instance_->message_channel().np_object());
+  // The object is expected to be retained before it is returned.
+  WebKit::WebBindings::retainObject(message_channel_np_object);
+  return message_channel_np_object;
 }
 
 void WebPluginImpl::paint(WebCanvas* canvas, const WebRect& rect) {