Use a mock WebAudioDevice for layout tests

content/public/renderer/content_renderer_client.h

Index: content/public/renderer/content_renderer_client.h
diff --git a/content/public/renderer/content_renderer_client.h b/content/public/renderer/content_renderer_client.h
index de1ecfc62ea9902cfb5491fc5723e3a653d87d57..6b5a8365d6f9a41028c26bf68fe97e542fb66709 100644
--- a/content/public/renderer/content_renderer_client.h
+++ b/content/public/renderer/content_renderer_client.h
@@ -26,6 +26,7 @@ class MessageLoop;
 }
 
 namespace WebKit {
+class WebAudioDevice;
 class WebClipboard;
 class WebFrame;
 class WebHyphenator;
@@ -141,6 +142,11 @@ class CONTENT_EXPORT ContentRendererClient {
   virtual WebKit::WebMIDIAccessor* OverrideCreateMIDIAccessor(
       WebKit::WebMIDIAccessorClient* client);
 
+  // Allows the embedder to override creating a WebAudioDevice.  If it
+  // returns NULL the content layer will create the audio device.
+  virtual WebKit::WebAudioDevice* OverrideCreateAudioDevice(
+      double sample_rate);
+
   // Allows the embedder to override the WebKit::WebClipboard used. If it
   // returns NULL the content layer will handle clipboard interactions.
   virtual WebKit::WebClipboard* OverrideWebClipboard();