Conditionally add compile-time enable for web audio on Mac OS X...

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/Source/WebKit/chromium/features.gypi.
 {
   'variables': {
     # WARNING: This list of strings completely replaces the list in
@@ skipping 62 matching lines @@
     'enable_touch_events%': '<(enable_touch_events)',
     'conditions': [
       ['(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,
       }],
+      ['OS=="mac"', {
+        'feature_defines': [
+          'ENABLE_WEB_AUDIO=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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