Make HandleWatcher watch on the same thread if the thread is running a MessagePumpMojo.

mojo/common/handle_watcher.h

 // Copyright 2013 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 MOJO_COMMON_HANDLE_WATCHER_H_
 #define MOJO_COMMON_HANDLE_WATCHER_H_
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 30 matching lines @@
   void Start(const Handle& handle,
              MojoHandleSignals handle_signals,
              MojoDeadline deadline,
              const base::Callback<void(MojoResult)>& callback);
 
   // Stops listening. Does nothing if not in the process of listening. Blocks
   // until no longer listening on the handle.
   void Stop();
 
  private:
-  class State;
+  class StateBase;
+  class SameThreadWatchingState;
+  class SecondaryThreadWatchingState;
 
   // If non-NULL Start() has been invoked.
-  scoped_ptr<State> state_;
+  scoped_ptr<StateBase> state_;
 
   DISALLOW_COPY_AND_ASSIGN(HandleWatcher);
 };
 
 }  // namespace common
 }  // namespace mojo
 
 #endif  // MOJO_COMMON_HANDLE_WATCHER_H_