Move MockFFmpeg instance setting into the constructor/destructor.

media/base/mock_ffmpeg.h

Index: media/base/mock_ffmpeg.h
===================================================================
--- media/base/mock_ffmpeg.h	(revision 75179)
+++ media/base/mock_ffmpeg.h	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -65,8 +65,7 @@
   // Used for verifying check points during tests.
   MOCK_METHOD1(CheckPoint, void(int id));
 
-  // Setter/getter for the global instance of MockFFmpeg.
-  static void set(MockFFmpeg* instance);
+  // Returns the current MockFFmpeg instance.
   static MockFFmpeg* get();
 
   // Returns the URLProtocol registered by the FFmpegGlue singleton.