[PPAPI] Documentation fixes.

ppapi/api/ppb_message_loop.idl

 /* 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.
  */
 
 /**
  * Defines the PPB_MessageLoop interface.
  */
 label Chrome {
   M25 = 1.0
@@ skipping 19 matching lines @@
  *    - Create the thread yourself (using pthreads).
  *    - Create the message loop resource.
  *    - Pass the message loop resource to your thread's main function.
  *    - Call PostWork() on the message loop to run functions on the thread.
  *
  *   From the background thread's main function:
  *    - Call AttachToCurrentThread() with the message loop resource.
  *    - Call Run() with the message loop resource.
  *
  *   Your callbacks should look like this:
+ *      @code
  *      void DoMyWork(void* user_data, int32_t status) {
  *        if (status != PP_OK) {
  *          Cleanup();  // e.g. free user_data.
  *          return;
  *        }
  *        ... do your work...
  *      }
+ *      @endcode
  * For a C++ example, see ppapi/utility/threading/simple_thread.h
  *
  * (You can also create the message loop resource on the background thread,
  * but then the main thread will have no reference to it should you want to
  * call PostWork()).
  *
  *
  * THREAD HANDLING
  *
  * The main thread has an implicitly created message loop. The main thread is
@@ skipping 203 matching lines @@
    *
    * @return
    *   - PP_OK: The request to quit was successfully posted.
    *   - PP_ERROR_BADRESOURCE: The message loop was invalid.
    *   - PP_ERROR_WRONG_THREAD: You are attempting to quit the main thread.
    *     The main thread's message loop is managed by the system and can't be
    *     quit.
    */
   int32_t PostQuit([in] PP_Resource message_loop, PP_Bool should_destroy);
 };