Revert 177842. This doesn't build in standalone webkit builds:

chrome/browser/about_flags.cc

 // 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.
 
 #include "chrome/browser/about_flags.h"
 
 #include <algorithm>
 #include <iterator>
 #include <map>
 #include <set>
@@ skipping 639 matching lines @@
     kOsAll,
     SINGLE_VALUE_TYPE(switches::kEnableEncryptedMedia)
   },
   {
     "enable-opus-playback",
     IDS_FLAGS_ENABLE_OPUS_PLAYBACK_NAME,
     IDS_FLAGS_ENABLE_OPUS_PLAYBACK_DESCRIPTION,
     kOsAll,
     SINGLE_VALUE_TYPE(switches::kEnableOpusPlayback)
   },
-  {
-    "enable-vp9-playback",
-    IDS_FLAGS_ENABLE_VP9_PLAYBACK_NAME,
-    IDS_FLAGS_ENABLE_VP9_PLAYBACK_DESCRIPTION,
-    kOsAll,
-    SINGLE_VALUE_TYPE(switches::kEnableVp9Playback)
-  },
 #if defined(USE_ASH)
   {
     "ash-disable-auto-window-placement",
     IDS_FLAGS_ASH_AUTO_WINDOW_PLACEMENT_NAME,
     IDS_FLAGS_ASH_AUTO_WINDOW_PLACEMENT_DESCRIPTION,
     kOsWin | kOsLinux | kOsCrOS,
     SINGLE_VALUE_TYPE(ash::switches::kAshDisableAutoWindowPlacement)
   },
   {
     "ash-enable-per-app-launcher",
@@ skipping 989 matching lines @@
 }
 
 const Experiment* GetExperiments(size_t* count) {
   *count = num_experiments;
   return experiments;
 }
 
 }  // namespace testing
 
 }  // namespace about_flags