Let use_accelerated_compositing be usable for both enabling and disabling compositing

build/features_override.gypi

 # Copyright (c) 2009 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.
 
 # This file is only included in full-chromium builds, and overrides the
 # feature_defines variable in third_party/WebKit/WebKit/chromium/features.gypi.
 {
   'variables': {
     # WARNING: This list of strings completely replaces the list in
     # features.gypi. Therefore, if an enable is listed in features.gypi
@@ skipping 39 matching lines @@
       'ENABLE_VIDEO=1',
       'ENABLE_WEB_SOCKETS=1',
       'ENABLE_WEB_TIMING=1',
       'ENABLE_WORKERS=1',
       'ENABLE_XPATH=1',
       'ENABLE_XSLT=1',
     ],
     # We have to nest variables inside variables so that they can be overridden
     # through GYP_DEFINES.
     'variables': {
-      'use_accelerated_compositing%': 0,
+      'use_accelerated_compositing%': 1,
       'enable_svg%': 1,
       'enable_touch_events%': 1,
     },
     'use_accelerated_compositing%': '<(use_accelerated_compositing)',
     'enable_svg%': '<(enable_svg)',
     'enable_touch_events%': '<(enable_touch_events)',
     'conditions': [
-      ['OS=="win" or OS=="linux" or OS=="mac" or use_accelerated_compositing==1', {
+      ['(OS=="win" or OS=="linux" or OS=="mac") and use_accelerated_compositing==1', {
         'feature_defines': [
           'WTF_USE_ACCELERATED_COMPOSITING=1',
           'ENABLE_3D_RENDERING=1',
           'ENABLE_ACCELERATED_2D_CANVAS=1',
         ],
         'use_accelerated_compositing': 1,
       }],
     ],
     # TODO: If the need arises, create a mechanism that will intelligently
     # merge the lists rather than replace one with the other. This may
     # require changes in gyp.
   },
 
 }
 
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