Add PluginMessageLoopProxy and use it for Host plugin UI thread.

The new class will also be used in the client plugin for the main plugin thread.

BUG=None
TEST=Everything works.

Review URL: http://codereview.chromium.org/7635030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97060 0039d316-1c4b-4281-b951-d872f2087c98

14 files changed, 317 insertions, 133 deletions

diff --git a/remoting/base/plugin_message_loop_proxy.cc b/remoting/base/plugin_message_loop_proxy.cc
new file mode 100644
index 0000000..0f6c668
--- /dev/null
+++ b/remoting/base/plugin_message_loop_proxy.cc
@@ -0,0 +1,114 @@
+// 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 "remoting/base/plugin_message_loop_proxy.h"
+
+namespace remoting {
+
+PluginMessageLoopProxy::PluginMessageLoopProxy(Delegate* delegate)
+    : delegate_(delegate) {
+}
+
+PluginMessageLoopProxy::~PluginMessageLoopProxy() {
+}
+
+void PluginMessageLoopProxy::Detach() {
+  base::AutoLock auto_lock(lock_);
+  delegate_ = NULL;
+}
+
+// MessageLoopProxy interface implementation.
+bool PluginMessageLoopProxy::PostTask(
+    const tracked_objects::Location& from_here,
+    Task* task) {
+  return PostDelayedTask(from_here, task, 0);
+}
+
+bool PluginMessageLoopProxy::PostDelayedTask(
+    const tracked_objects::Location& from_here,
+    Task* task,
+    int64 delay_ms) {
+  base::AutoLock auto_lock(lock_);
+  if (!delegate_) {
+    return false;
+  } else {
+    return delegate_->RunOnPluginThread(
+        delay_ms, &PluginMessageLoopProxy::RunTask, task);
+  }
+}
+
+bool PluginMessageLoopProxy::PostNonNestableTask(
+    const tracked_objects::Location& from_here,
+    Task* task) {
+  // All tasks running on this message loop are non-nestable.
+  return PostTask(from_here, task);
+}
+
+bool PluginMessageLoopProxy::PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      Task* task,
+      int64 delay_ms) {
+  // All tasks running on this message loop are non-nestable.
+  return PostDelayedTask(from_here, task, delay_ms);
+}
+
+bool PluginMessageLoopProxy::PostTask(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task) {
+  return PostDelayedTask(from_here, task, 0);
+}
+
+bool PluginMessageLoopProxy::PostDelayedTask(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task,
+    int64 delay_ms) {
+  base::AutoLock auto_lock(lock_);
+  if (!delegate_) {
+    return false;
+  } else {
+    base::Closure* task_on_heap = new base::Closure(task);
+    return delegate_->RunOnPluginThread(
+        delay_ms, &PluginMessageLoopProxy::RunClosure, task_on_heap);
+  }
+}
+
+bool PluginMessageLoopProxy::PostNonNestableTask(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task) {
+  // All tasks running on this message loop are non-nestable.
+  return PostTask(from_here, task);
+}
+
+bool PluginMessageLoopProxy::PostNonNestableDelayedTask(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task,
+    int64 delay_ms) {
+  // All tasks running on this message loop are non-nestable.
+  return PostDelayedTask(from_here, task, delay_ms);
+}
+
+bool PluginMessageLoopProxy::BelongsToCurrentThread() {
+  base::AutoLock auto_lock(lock_);
+  if (delegate_) {
+    return delegate_->IsPluginThread();
+  } else {
+    return false;
+  }
+}
+
+// static
+void PluginMessageLoopProxy::RunTask(void* data) {
+  Task* task = reinterpret_cast<Task*>(data);
+  task->Run();
+  delete task;
+}
+
+// static
+void PluginMessageLoopProxy::RunClosure(void* data) {
+  base::Closure* task = reinterpret_cast<base::Closure*>(data);
+  task->Run();
+  delete task;
+}
+
+}  // namespace remoting
diff --git a/remoting/base/plugin_message_loop_proxy.h b/remoting/base/plugin_message_loop_proxy.h
new file mode 100644
index 0000000..7b2eef2
--- /dev/null
+++ b/remoting/base/plugin_message_loop_proxy.h
@@ -0,0 +1,80 @@
+// 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 REMOTING_BASE_PLUGIN_MESSAGE_LOOP_H_
+#define REMOTING_BASE_PLUGIN_MESSAGE_LOOP_H_
+
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/message_loop_proxy.h"
+#include "base/synchronization/lock.h"
+
+namespace remoting {
+
+// MessageLoopProxy for plugin main threads.
+class PluginMessageLoopProxy : public base::MessageLoopProxy {
+ public:
+  class Delegate {
+   public:
+    Delegate() { }
+    virtual ~Delegate() { }
+
+    virtual bool RunOnPluginThread(
+        int delay_ms, void(function)(void*), void* data) = 0;
+    virtual bool IsPluginThread() = 0;
+  };
+
+  // Caller keeps ownership of delegate.
+  PluginMessageLoopProxy(Delegate* delegate);
+  virtual ~PluginMessageLoopProxy();
+
+  void Detach();
+
+  // base::MessageLoopProxy interface.
+  virtual bool PostTask(
+      const tracked_objects::Location& from_here,
+      Task* task) OVERRIDE;
+  virtual bool PostDelayedTask(
+      const tracked_objects::Location& from_here,
+      Task* task,
+      int64 delay_ms) OVERRIDE;
+  virtual bool PostNonNestableTask(
+      const tracked_objects::Location& from_here,
+      Task* task) OVERRIDE;
+  virtual bool PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      Task* task,
+      int64 delay_ms) OVERRIDE;
+
+  virtual bool PostTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task) OVERRIDE;
+  virtual bool PostDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      int64 delay_ms) OVERRIDE;
+  virtual bool PostNonNestableTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task) OVERRIDE;
+  virtual bool PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      int64 delay_ms) OVERRIDE;
+
+  virtual bool BelongsToCurrentThread() OVERRIDE;
+
+ private:
+  // |lock_| must be acquired when accessing |delegate_|.
+  base::Lock lock_;
+  Delegate* delegate_;
+
+  static void RunTask(void* data);
+  static void RunClosure(void* data);
+
+  DISALLOW_COPY_AND_ASSIGN(PluginMessageLoopProxy);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_BASE_PLUGIN_MESSAGE_LOOP_H_
diff --git a/remoting/host/chromoting_host_context.cc b/remoting/host/chromoting_host_context.cc
index de99a1f..6f02943 100644
--- a/remoting/host/chromoting_host_context.cc
+++ b/remoting/host/chromoting_host_context.cc
@@ -12,10 +12,12 @@
 
 namespace remoting {
 
-ChromotingHostContext::ChromotingHostContext()
+ChromotingHostContext::ChromotingHostContext(
+    base::MessageLoopProxy* ui_message_loop)
     : main_thread_("ChromotingMainThread"),
       encode_thread_("ChromotingEncodeThread"),
-      desktop_thread_("ChromotingDesktopThread") {
+      desktop_thread_("ChromotingDesktopThread"),
+      ui_message_loop_(ui_message_loop) {
 }
 
 ChromotingHostContext::~ChromotingHostContext() {
@@ -41,6 +43,10 @@ JingleThread* ChromotingHostContext::jingle_thread() {
   return &jingle_thread_;
 }
 
+base::MessageLoopProxy* ChromotingHostContext::ui_message_loop() {
+  return ui_message_loop_;
+}
+
 MessageLoop* ChromotingHostContext::main_message_loop() {
   return main_thread_.message_loop();
 }
@@ -57,31 +63,4 @@ MessageLoop* ChromotingHostContext::desktop_message_loop() {
   return desktop_thread_.message_loop();
 }
 
-void ChromotingHostContext::SetUITaskPostFunction(
-    const UIThreadPostTaskFunction& poster) {
-  ui_poster_ = poster;
-  ui_main_thread_id_ = base::PlatformThread::CurrentId();
-}
-
-void ChromotingHostContext::PostTaskToUIThread(
-    const tracked_objects::Location& from_here, const base::Closure& task) {
-  ui_poster_.Run(from_here, task);
-}
-
-void ChromotingHostContext::PostDelayedTaskToUIThread(
-    const tracked_objects::Location& from_here,
-    const base::Closure& task,
-    int delay_ms) {
-  // Post delayed task on the main thread that will post task on UI
-  // thread. It is safe to use base::Unretained() here because
-  // ChromotingHostContext owns |main_thread_|.
-  main_message_loop()->PostDelayedTask(from_here, base::Bind(
-      &ChromotingHostContext::PostTaskToUIThread, base::Unretained(this),
-      from_here, task), delay_ms);
-}
-
-bool ChromotingHostContext::IsUIThread() const {
-  return ui_main_thread_id_ == base::PlatformThread::CurrentId();
-}
-
 }  // namespace remoting
diff --git a/remoting/host/chromoting_host_context.h b/remoting/host/chromoting_host_context.h
index 38f1cae..d2ab3e6 100644
--- a/remoting/host/chromoting_host_context.h
+++ b/remoting/host/chromoting_host_context.h
@@ -25,12 +25,8 @@ namespace remoting {
 // process.  This class is virtual only for testing purposes (see below).
 class ChromotingHostContext {
  public:
-  typedef base::Callback<void(
-      const tracked_objects::Location& from_here,
-      const base::Closure& task)> UIThreadPostTaskFunction;
-
   // Create a context.
-  ChromotingHostContext();
+  ChromotingHostContext(base::MessageLoopProxy* ui_message_loop);
   virtual ~ChromotingHostContext();
 
   // TODO(ajwong): Move the Start/Stop methods out of this class. Then
@@ -42,21 +38,12 @@ class ChromotingHostContext {
 
   virtual JingleThread* jingle_thread();
 
+  virtual base::MessageLoopProxy* ui_message_loop();
   virtual MessageLoop* main_message_loop();
   virtual MessageLoop* encode_message_loop();
   virtual base::MessageLoopProxy* network_message_loop();
   virtual MessageLoop* desktop_message_loop();
 
-  // Must be called from the main GUI thread.
-  void SetUITaskPostFunction(const UIThreadPostTaskFunction& poster);
-
-  void PostTaskToUIThread(const tracked_objects::Location& from_here,
-                          const base::Closure& task);
-  void PostDelayedTaskToUIThread(const tracked_objects::Location& from_here,
-                                 const base::Closure& task,
-                                 int delay_ms);
-  bool IsUIThread() const;
-
  private:
   FRIEND_TEST_ALL_PREFIXES(ChromotingHostContextTest, StartAndStop);
 
@@ -73,10 +60,7 @@ class ChromotingHostContext {
   // This is NOT a Chrome-style UI thread.
   base::Thread desktop_thread_;
 
-  UIThreadPostTaskFunction ui_poster_;
-  // This IS the main Chrome GUI thread that |ui_poster_| will post to.
-  base::PlatformThreadId ui_main_thread_id_;
-
+  scoped_refptr<base::MessageLoopProxy> ui_message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromotingHostContext);
 };
diff --git a/remoting/host/chromoting_host_context_unittest.cc b/remoting/host/chromoting_host_context_unittest.cc
index 21bcab8..3d857b3 100644
--- a/remoting/host/chromoting_host_context_unittest.cc
+++ b/remoting/host/chromoting_host_context_unittest.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/message_loop.h"
+#include "base/message_loop_proxy.h"
 #include "remoting/host/chromoting_host_context.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -11,7 +12,10 @@ namespace remoting {
 // A simple test that starts and stop the context. This tests the context
 // operates properly and all threads and message loops are valid.
 TEST(ChromotingHostContextTest, StartAndStop) {
-  ChromotingHostContext context;
+  MessageLoop message_loop;
+  ChromotingHostContext context(
+      base::MessageLoopProxy::current());
+
   context.Start();
   EXPECT_TRUE(context.jingle_thread());
   EXPECT_TRUE(context.main_message_loop());
diff --git a/remoting/host/chromoting_host_unittest.cc b/remoting/host/chromoting_host_unittest.cc
index 129d922..0842832 100644
--- a/remoting/host/chromoting_host_unittest.cc
+++ b/remoting/host/chromoting_host_unittest.cc
@@ -78,7 +78,7 @@ class ChromotingHostTest : public testing::Test {
     ON_CALL(context_, network_message_loop())
         .WillByDefault(Return(message_loop_proxy_.get()));
     ON_CALL(context_, ui_message_loop())
-        .WillByDefault(Return(&message_loop_));
+        .WillByDefault(Return(message_loop_proxy_.get()));
     EXPECT_CALL(context_, main_message_loop())
         .Times(AnyNumber());
     EXPECT_CALL(context_, encode_message_loop())
@@ -88,12 +88,6 @@ class ChromotingHostTest : public testing::Test {
     EXPECT_CALL(context_, ui_message_loop())
         .Times(AnyNumber());
 
-    context_.SetUITaskPostFunction(base::Bind(
-        static_cast<void(MessageLoop::*)(
-            const tracked_objects::Location&,
-            const base::Closure&)>(&MessageLoop::PostTask),
-        base::Unretained(&message_loop_)));
-
     Capturer* capturer = new CapturerFake();
     event_executor_ = new MockEventExecutor();
     curtain_ = new MockCurtain();
diff --git a/remoting/host/desktop_environment.cc b/remoting/host/desktop_environment.cc
index 8377ac7..bdc7ded 100644
--- a/remoting/host/desktop_environment.cc
+++ b/remoting/host/desktop_environment.cc
@@ -23,21 +23,30 @@ namespace remoting {
 // thread. This is neccessary so that DesktopEnvironment can be
 // deleted synchronously even while there are pending tasks on the
 // message queue.
+//
+// TODO(sergeyu): Merge this code with remoting::TaskThreadProxy. The
+// problem solved by this class is very simular to the one solved by
+// ScopedRunnableMethodFactory. The main difference is that this class
+// is thread-safe. Change the interface to make it look more like
+// ScopedRunnableMethodFactory and rename it to avoid confusion with
+// MessageLoopProxy.
 class UIThreadProxy : public base::RefCountedThreadSafe<UIThreadProxy> {
  public:
-  UIThreadProxy(ChromotingHostContext* context)
-      : context_(context) {
+  UIThreadProxy(base::MessageLoopProxy* message_loop)
+      : message_loop_(message_loop) {
   }
 
+  // TODO(sergeyu): Rename this method.
   void Detach() {
-    DCHECK(context_->IsUIThread());
-    context_ = NULL;
+    DCHECK(message_loop_->BelongsToCurrentThread());
+    message_loop_ = NULL;
   }
 
   void CallOnUIThread(const tracked_objects::Location& from_here,
                       const base::Closure& closure) {
-    if (context_) {
-      context_->PostTaskToUIThread(from_here, base::Bind(
+    scoped_refptr<base::MessageLoopProxy> message_loop = message_loop_;
+    if (message_loop) {
+      message_loop->PostTask(from_here, base::Bind(
           &UIThreadProxy::CallClosure, this, closure));
     }
   }
@@ -45,8 +54,9 @@ class UIThreadProxy : public base::RefCountedThreadSafe<UIThreadProxy> {
   void CallOnUIThreadDelayed(const tracked_objects::Location& from_here,
                              const base::Closure& closure,
                              int delay_ms) {
-    if (context_) {
-      context_->PostDelayedTaskToUIThread(from_here, base::Bind(
+    scoped_refptr<base::MessageLoopProxy> message_loop = message_loop_;
+    if (message_loop) {
+      message_loop->PostDelayedTask(from_here, base::Bind(
           &UIThreadProxy::CallClosure, this, closure), delay_ms);
     }
   }
@@ -57,11 +67,11 @@ class UIThreadProxy : public base::RefCountedThreadSafe<UIThreadProxy> {
   virtual ~UIThreadProxy() { }
 
   void CallClosure(const base::Closure& closure) {
-    if (context_)
+    if (message_loop_)
       closure.Run();
   }
 
-  ChromotingHostContext* context_;
+  scoped_refptr<base::MessageLoopProxy> message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(UIThreadProxy);
 };
@@ -98,14 +108,14 @@ DesktopEnvironment::DesktopEnvironment(ChromotingHostContext* context,
       local_input_monitor_(local_input_monitor),
       is_monitoring_local_inputs_(false),
       continue_timer_started_(false),
-      proxy_(new UIThreadProxy(context)) {
+      proxy_(new UIThreadProxy(context->ui_message_loop())) {
 }
 
 DesktopEnvironment::~DesktopEnvironment() {
 }
 
 void DesktopEnvironment::Shutdown() {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   MonitorLocalInputs(false);
   ShowDisconnectWindow(false, std::string());
@@ -131,7 +141,7 @@ void DesktopEnvironment::OnPause(bool pause) {
 }
 
 void DesktopEnvironment::ProcessOnConnect(const std::string& username) {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   MonitorLocalInputs(true);
   ShowDisconnectWindow(true, username);
@@ -139,7 +149,7 @@ void DesktopEnvironment::ProcessOnConnect(const std::string& username) {
 }
 
 void DesktopEnvironment::ProcessOnLastDisconnect() {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   MonitorLocalInputs(false);
   ShowDisconnectWindow(false, std::string());
@@ -152,7 +162,7 @@ void DesktopEnvironment::ProcessOnPause(bool pause) {
 }
 
 void DesktopEnvironment::MonitorLocalInputs(bool enable) {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   if (enable == is_monitoring_local_inputs_)
     return;
@@ -166,7 +176,7 @@ void DesktopEnvironment::MonitorLocalInputs(bool enable) {
 
 void DesktopEnvironment::ShowDisconnectWindow(bool show,
                                               const std::string& username) {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   if (show) {
     disconnect_window_->Show(host_, username);
@@ -176,7 +186,7 @@ void DesktopEnvironment::ShowDisconnectWindow(bool show,
 }
 
 void DesktopEnvironment::ShowContinueWindow(bool show) {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   if (show) {
     continue_window_->Show(host_);
@@ -186,7 +196,7 @@ void DesktopEnvironment::ShowContinueWindow(bool show) {
 }
 
 void DesktopEnvironment::StartContinueWindowTimer(bool start) {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   if (start && !continue_timer_started_) {
     continue_timer_target_time_ = base::Time::Now() +
@@ -201,7 +211,7 @@ void DesktopEnvironment::StartContinueWindowTimer(bool start) {
 }
 
 void DesktopEnvironment::ContinueWindowTimerFunc() {
-  DCHECK(context_->IsUIThread());
+  DCHECK(context_->ui_message_loop()->BelongsToCurrentThread());
 
   // This function may be called prematurely if timer was stopped and
   // then started again. In that case we just ignore this call.
diff --git a/remoting/host/host_mock_objects.cc b/remoting/host/host_mock_objects.cc
index de0ea97..1af08ee 100644
--- a/remoting/host/host_mock_objects.cc
+++ b/remoting/host/host_mock_objects.cc
@@ -4,6 +4,8 @@
 
 #include "remoting/host/host_mock_objects.h"
 
+#include "base/message_loop_proxy.h"
+
 namespace remoting {
 
 MockCapturer::MockCapturer() {}
@@ -46,7 +48,9 @@ LocalInputMonitor* LocalInputMonitor::Create() {
   return new MockLocalInputMonitor();
 }
 
-MockChromotingHostContext::MockChromotingHostContext() {}
+MockChromotingHostContext::MockChromotingHostContext()
+    : ChromotingHostContext(base::MessageLoopProxy::current()) {
+}
 
 MockChromotingHostContext::~MockChromotingHostContext() {}
 
diff --git a/remoting/host/host_mock_objects.h b/remoting/host/host_mock_objects.h
index 5a627ea..67aed7c 100644
--- a/remoting/host/host_mock_objects.h
+++ b/remoting/host/host_mock_objects.h
@@ -81,10 +81,10 @@ class MockChromotingHostContext : public ChromotingHostContext {
   MOCK_METHOD0(Start, void());
   MOCK_METHOD0(Stop, void());
   MOCK_METHOD0(jingle_thread, JingleThread*());
+  MOCK_METHOD0(ui_message_loop, base::MessageLoopProxy*());
   MOCK_METHOD0(main_message_loop, MessageLoop*());
   MOCK_METHOD0(encode_message_loop, MessageLoop*());
   MOCK_METHOD0(network_message_loop, base::MessageLoopProxy*());
-  MOCK_METHOD0(ui_message_loop, MessageLoop*());
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MockChromotingHostContext);
diff --git a/remoting/host/plugin/host_plugin.cc b/remoting/host/plugin/host_plugin.cc
index f901a03..0776372 100644
--- a/remoting/host/plugin/host_plugin.cc
+++ b/remoting/host/plugin/host_plugin.cc
@@ -12,6 +12,7 @@
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/stringize_macros.h"
+#include "remoting/base/plugin_message_loop_proxy.h"
 #include "remoting/host/plugin/host_plugin_utils.h"
 #include "remoting/host/plugin/host_script_object.h"
 #include "third_party/npapi/bindings/npapi.h"
@@ -58,7 +59,7 @@ base::AtExitManager* g_at_exit_manager = NULL;
 // NPAPI plugin implementation for remoting host.
 // Documentation for most of the calls in this class can be found here:
 // https://developer.mozilla.org/en/Gecko_Plugin_API_Reference/Scripting_plugins
-class HostNPPlugin {
+class HostNPPlugin : public remoting::PluginMessageLoopProxy::Delegate {
  public:
   // |mode| is the display mode of plug-in. Values:
   // NP_EMBED: (1) Instance was created by an EMBED tag and shares the browser
@@ -66,7 +67,10 @@ class HostNPPlugin {
   // NP_FULL: (2) Instance was created by a separate file and is the primary
   //              content in the window.
   HostNPPlugin(NPP instance, uint16 mode)
-    : instance_(instance), scriptable_object_(NULL) {}
+      : instance_(instance),
+        scriptable_object_(NULL),
+        np_thread_id_(base::PlatformThread::CurrentId()) {
+  }
 
   ~HostNPPlugin() {
     if (scriptable_object_) {
@@ -146,11 +150,49 @@ class HostNPPlugin {
     return scriptable_object_;
   }
 
+  // PluginMessageLoopProxy::Delegate implementation.
+  virtual bool RunOnPluginThread(
+      int delay_ms, void(function)(void*), void* data) OVERRIDE {
+    if (delay_ms == 0) {
+      g_npnetscape_funcs->pluginthreadasynccall(instance_, function, data);
+    } else {
+      base::AutoLock auto_lock(timers_lock_);
+      uint32_t timer_id = g_npnetscape_funcs->scheduletimer(
+          instance_, delay_ms, false, &NPDelayedTaskSpringboard);
+      DelayedTask task = {function, data};
+      timers_[timer_id] = task;
+    }
+    return true;
+  }
+
+  virtual bool IsPluginThread() OVERRIDE {
+    return np_thread_id_ == base::PlatformThread::CurrentId();
+  }
+
+  static void NPDelayedTaskSpringboard(NPP npp, uint32_t timer_id) {
+    HostNPPlugin* self = reinterpret_cast<HostNPPlugin*>(npp->pdata);
+    DelayedTask task;
+    {
+      base::AutoLock auto_lock(self->timers_lock_);
+      std::map<uint32_t, DelayedTask>::iterator it =
+          self->timers_.find(timer_id);
+      CHECK(it != self->timers_.end());
+      task = it->second;
+      self->timers_.erase(it);
+    }
+    task.function(task.data);
+  }
+
  private:
   struct ScriptableNPObject : public NPObject {
     HostNPScriptObject* scriptable_object;
   };
 
+  struct DelayedTask {
+    void (*function)(void*);
+    void* data;
+  };
+
   static HostNPScriptObject* ScriptableFromObject(NPObject* obj) {
     return reinterpret_cast<ScriptableNPObject*>(obj)->scriptable_object;
   }
@@ -160,10 +202,11 @@ class HostNPPlugin {
     ScriptableNPObject* object =
         reinterpret_cast<ScriptableNPObject*>(
             g_npnetscape_funcs->memalloc(sizeof(ScriptableNPObject)));
+    HostNPPlugin* plugin = reinterpret_cast<HostNPPlugin*>(npp->pdata);
 
     object->_class = aClass;
     object->referenceCount = 1;
-    object->scriptable_object = new HostNPScriptObject(npp, object);
+    object->scriptable_object = new HostNPScriptObject(npp, object, plugin);
     if (!object->scriptable_object->Init()) {
       Deallocate(object);
       object = NULL;
@@ -290,6 +333,10 @@ class HostNPPlugin {
 
   NPP instance_;
   NPObject* scriptable_object_;
+
+  base::PlatformThreadId np_thread_id_;
+  std::map<uint32_t, DelayedTask> timers_;
+  base::Lock timers_lock_;
 };
 
 // Utility functions to map NPAPI Entry Points to C++ Objects.
diff --git a/remoting/host/plugin/host_script_object.cc b/remoting/host/plugin/host_script_object.cc
index 8b100c4..5d26050 100644
--- a/remoting/host/plugin/host_script_object.cc
+++ b/remoting/host/plugin/host_script_object.cc
@@ -78,11 +78,17 @@ static bool g_logging_to_plugin = false;
 static HostNPScriptObject* g_logging_scriptable_object = NULL;
 static logging::LogMessageHandlerFunction g_logging_old_handler = NULL;
 
-HostNPScriptObject::HostNPScriptObject(NPP plugin, NPObject* parent)
+HostNPScriptObject::HostNPScriptObject(
+    NPP plugin,
+    NPObject* parent,
+    PluginMessageLoopProxy::Delegate* plugin_thread_delegate)
     : plugin_(plugin),
       parent_(parent),
       state_(kDisconnected),
       np_thread_id_(base::PlatformThread::CurrentId()),
+      plugin_message_loop_proxy_(
+          new PluginMessageLoopProxy(plugin_thread_delegate)),
+      host_context_(plugin_message_loop_proxy_),
       failed_login_attempts_(0),
       disconnected_event_(true, false),
       nat_traversal_enabled_(false),
@@ -99,10 +105,6 @@ HostNPScriptObject::HostNPScriptObject(NPP plugin, NPObject* parent)
     g_logging_old_handler = logging::GetLogMessageHandler();
   logging::SetLogMessageHandler(&LogToUI);
   g_logging_scriptable_object = this;
-
-  VLOG(2) << "HostNPScriptObject";
-  host_context_.SetUITaskPostFunction(base::Bind(
-      &HostNPScriptObject::PostTaskToNPThread, base::Unretained(this)));
 }
 
 HostNPScriptObject::~HostNPScriptObject() {
@@ -116,6 +118,8 @@ HostNPScriptObject::~HostNPScriptObject() {
   g_logging_old_handler = NULL;
   g_logging_scriptable_object = NULL;
 
+  plugin_message_loop_proxy_->Detach();
+
   // Stop listening for policy updates.
   if (nat_policy_.get()) {
     base::WaitableEvent nat_policy_stopped_(true, false);
@@ -128,7 +132,6 @@ HostNPScriptObject::~HostNPScriptObject() {
   // here because |host_context_| needs to be stopped on the plugin
   // thread, but the plugin thread may not exist after the instance
   // is destroyed.
-  destructing_.Set();
   disconnected_event_.Reset();
   DisconnectInternal();
   disconnected_event_.Wait();
@@ -577,11 +580,8 @@ void HostNPScriptObject::OnReceivedSupportID(
 }
 
 void HostNPScriptObject::OnStateChanged(State state) {
-  if (destructing_.IsSet())
-    return;
-
-  if (!host_context_.IsUIThread()) {
-    host_context_.PostTaskToUIThread(
+  if (!plugin_message_loop_proxy_->BelongsToCurrentThread()) {
+    plugin_message_loop_proxy_->PostTask(
         FROM_HERE, base::Bind(&HostNPScriptObject::OnStateChanged,
                               base::Unretained(this), state));
     return;
@@ -615,11 +615,8 @@ bool HostNPScriptObject::LogToUI(int severity, const char* file, int line,
 }
 
 void HostNPScriptObject::LogDebugInfo(const std::string& message) {
-  if (destructing_.IsSet())
-    return;
-
-  if (!host_context_.IsUIThread()) {
-    host_context_.PostTaskToUIThread(
+  if (!plugin_message_loop_proxy_->BelongsToCurrentThread()) {
+    plugin_message_loop_proxy_->PostTask(
         FROM_HERE, base::Bind(&HostNPScriptObject::LogDebugInfo,
                               base::Unretained(this), message));
     return;
@@ -704,25 +701,4 @@ bool HostNPScriptObject::InvokeAndIgnoreResult(NPObject* func,
   return is_good;
 }
 
-void HostNPScriptObject::PostTaskToNPThread(
-    const tracked_objects::Location& from_here, const base::Closure& task) {
-  // The NPAPI functions cannot make use of |from_here|, but this method is
-  // passed as a callback to ChromotingHostContext, so it needs to have the
-  // appropriate signature.
-
-  // Copy task to the heap so that we can pass it to NPTaskSpringboard().
-  base::Closure* task_in_heap = new base::Closure(task);
-
-  // Can be called from any thread.
-  g_npnetscape_funcs->pluginthreadasynccall(plugin_, &NPTaskSpringboard,
-                                            task_in_heap);
-}
-
-// static
-void HostNPScriptObject::NPTaskSpringboard(void* task) {
-  base::Closure* real_task = reinterpret_cast<base::Closure*>(task);
-  real_task->Run();
-  delete real_task;
-}
-
 }  // namespace remoting
diff --git a/remoting/host/plugin/host_script_object.h b/remoting/host/plugin/host_script_object.h
index 2d776ad..04a35b4 100644
--- a/remoting/host/plugin/host_script_object.h
+++ b/remoting/host/plugin/host_script_object.h
@@ -15,6 +15,7 @@
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 #include "base/time.h"
+#include "remoting/base/plugin_message_loop_proxy.h"
 #include "remoting/host/chromoting_host_context.h"
 #include "remoting/host/host_status_observer.h"
 #include "remoting/host/plugin/host_plugin_utils.h"
@@ -45,7 +46,8 @@ class NatPolicy;
 // destroyed it sychronously shuts down the host and all threads.
 class HostNPScriptObject : public HostStatusObserver {
  public:
-  HostNPScriptObject(NPP plugin, NPObject* parent);
+  HostNPScriptObject(NPP plugin, NPObject* parent,
+                     PluginMessageLoopProxy::Delegate* plugin_thread_delegate);
   virtual ~HostNPScriptObject();
 
   bool Init();
@@ -142,13 +144,6 @@ class HostNPScriptObject : public HostStatusObserver {
                              const NPVariant* args,
                              uint32_t argCount);
 
-  // Posts a task on the main NP thread.
-  void PostTaskToNPThread(
-      const tracked_objects::Location& from_here, const base::Closure& task);
-
-  // Utility function for PostTaskToNPThread.
-  static void NPTaskSpringboard(void* task);
-
   // Set an exception for the current call.
   void SetException(const std::string& exception_string);
 
@@ -162,6 +157,7 @@ class HostNPScriptObject : public HostStatusObserver {
   ScopedRefNPObject log_debug_info_func_;
   ScopedRefNPObject on_state_changed_func_;
   base::PlatformThreadId np_thread_id_;
+  scoped_refptr<PluginMessageLoopProxy> plugin_message_loop_proxy_;
 
   scoped_ptr<RegisterSupportHostRequest> register_request_;
   scoped_refptr<MutableHostConfig> host_config_;
@@ -172,7 +168,6 @@ class HostNPScriptObject : public HostStatusObserver {
   int failed_login_attempts_;
 
   base::WaitableEvent disconnected_event_;
-  base::CancellationFlag destructing_;
 
   scoped_ptr<policy_hack::NatPolicy> nat_policy_;
 
diff --git a/remoting/host/simple_host_process.cc b/remoting/host/simple_host_process.cc
index 3e6000c..92b515e 100644
--- a/remoting/host/simple_host_process.cc
+++ b/remoting/host/simple_host_process.cc
@@ -104,13 +104,8 @@ class SimpleHost {
     // It needs to be a UI message loop to keep runloops spinning on the Mac.
     MessageLoop message_loop(MessageLoop::TYPE_UI);
 
-    remoting::ChromotingHostContext context;
-    // static_cast needed to resolve overloaded PostTask member-function.
-    context.SetUITaskPostFunction(base::Bind(
-        static_cast<void(MessageLoop::*)(
-            const tracked_objects::Location&,
-            const base::Closure&)>(&MessageLoop::PostTask),
-        base::Unretained(&message_loop)));
+    remoting::ChromotingHostContext context(
+        base::MessageLoopProxy::current());
     context.Start();
 
     base::Thread file_io_thread("FileIO");
diff --git a/remoting/remoting.gyp b/remoting/remoting.gyp
index 8d00dc7..6eb1c20 100644
--- a/remoting/remoting.gyp
+++ b/remoting/remoting.gyp
@@ -337,6 +337,8 @@
         'base/encoder_vp8.h',
         'base/encoder_row_based.cc',
         'base/encoder_row_based.h',
+        'base/plugin_message_loop_proxy.cc',
+        'base/plugin_message_loop_proxy.h',
         'base/rate_counter.cc',
         'base/rate_counter.h',
         'base/running_average.cc',