Revert 119198 - First pass at implementing the MessageLoop interface. This includes a simple

ppapi/thunk/ppb_message_loop_api.h

-// Copyright (c) 2012 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 PPAPI_THUNK_PPB_MESSAGE_LOOP_API_H_
-#define PPAPI_THUNK_PPB_MESSAGE_LOOP_API_H_
-
-namespace ppapi {
-namespace thunk {
-
-class PPB_MessageLoop_API {
- public:
-  virtual ~PPB_MessageLoop_API() {}
-
-  virtual int32_t AttachToCurrentThread() = 0;
-  virtual int32_t Run() = 0;
-  virtual int32_t PostWork(PP_CompletionCallback callback,
-                           int64_t delay_ms) = 0;
-  virtual int32_t PostQuit(PP_Bool should_destroy) = 0;
-};
-
-}  // namespace thunk
-}  // namespace ppapi
-
-#endif  // PPAPI_THUNK_PPB_MESSAGE_LOOP_API_H_