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

This is a more limited version of the patch already reviewed here:
http://codereview.chromium.org/6308014/
BUG=none
TEST=none
(tested locally on Mac OS X to verify build and that the feature could be enabled)
Review URL: http://codereview.chromium.org/6388002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@72306 0039d316-1c4b-4281-b951-d872f2087c98

build/features_override.gypi

@@ -80,6 +80,11 @@
         ],
         '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

chrome/renderer/render_thread.cc

@@ -937,10 +937,8 @@ void RenderThread::EnsureWebKitInitialized() {
   WebRuntimeFeatures::enableGeolocation(
       !command_line.HasSwitch(switches::kDisableGeolocation));
 
-#ifdef HAS_WEBAUDIO_RUNTIMEFEATURES
   WebRuntimeFeatures::enableWebAudio(
       command_line.HasSwitch(switches::kEnableWebAudio));
-#endif
 
   WebRuntimeFeatures::enableWebGL(
       !command_line.HasSwitch(switches::kDisable3DAPIs) &&

webkit/glue/webpreferences.cc

@@ -143,10 +143,8 @@ void WebPreferences::Apply(WebView* web_view) const {
   // but also because it cause a possible crash in Editor::hasBidiSelection().
   settings->setTextDirectionSubmenuInclusionBehaviorNeverIncluded();
 
-#ifdef HAS_WEBAUDIO_FEATURE_ENABLE
   // Enable the web audio API if requested on the command line.
   settings->setWebAudioEnabled(webaudio_enabled);
-#endif
 
   // Enable experimental WebGL support if requested on command line
   // and support is compiled in.