Add PluginMessageLoopProxy and use it for Host plugin UI thread.

remoting/host/chromoting_host_context.h

Index: remoting/host/chromoting_host_context.h
diff --git a/remoting/host/chromoting_host_context.h b/remoting/host/chromoting_host_context.h
index 0bd0f62d15322bf3e9c4baaf11cebf774b0325c2..d893d2011e4548ef304e96521cc92a94587856c9 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);
 
@@ -74,10 +61,7 @@ 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);
 };