Add PluginMessageLoopProxy and use it for Host plugin UI thread.

remoting/jingle_glue/jingle_thread.h

Index: remoting/jingle_glue/jingle_thread.h
diff --git a/remoting/jingle_glue/jingle_thread.h b/remoting/jingle_glue/jingle_thread.h
index 80924a21b4bba7010c539b723c291a2daa0e813c..35b46f2da8e379e7034effca79b4658c51e0feaa 100644
--- a/remoting/jingle_glue/jingle_thread.h
+++ b/remoting/jingle_glue/jingle_thread.h
@@ -12,13 +12,9 @@
 #include "third_party/libjingle/source/talk/base/taskrunner.h"
 #include "third_party/libjingle/source/talk/base/thread.h"
 
-namespace base {
-class MessageLoopProxy;
-}  // namespace base
-
 namespace buzz {
 class XmppClient;
-}  // namespace buzz
+}
 
 namespace remoting {
 
@@ -60,8 +56,9 @@ class JingleThread : public talk_base::Thread {
   virtual void Stop();
 
   // Returns Chromiums message loop for this thread.
+  // TODO(sergeyu): remove this method when we use base::Thread instead of
+  // talk_base::Thread
   MessageLoop* message_loop();
-  base::MessageLoopProxy* message_loop_proxy();
 
   // Returns task pump if the thread is running, otherwise NULL is returned.
   TaskPump* task_pump();
@@ -71,7 +68,6 @@ class JingleThread : public talk_base::Thread {
   base::WaitableEvent started_event_;
   base::WaitableEvent stopped_event_;
   MessageLoop* message_loop_;
-  scoped_refptr<base::MessageLoopProxy> message_loop_proxy_;
 
   DISALLOW_COPY_AND_ASSIGN(JingleThread);
 };