Implement web speech synthesis.

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index af10346b14b42ac5bdff3fd5032e4bbf772b6171..46ea4c62ca1234072431fb3471474441281411bd 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -76,6 +76,7 @@ class RenderViewHostDelegateView;
 class ResourceContext;
 class SiteInstance;
 class SpeechRecognitionManagerDelegate;
+class TtsDispatcherHostDelegate;
 class WebContents;
 class WebContentsViewDelegate;
 class WebContentsViewPort;
@@ -428,6 +429,10 @@ class CONTENT_EXPORT ContentBrowserClient {
   virtual SpeechRecognitionManagerDelegate*
       GetSpeechRecognitionManagerDelegate();
 
+  // Allows the embedder to return a delegate for the TtsDispatcherHost.
+  // The delegate will be owned by the dispatcher. It's valid to return NULL.
+  virtual TtsDispatcherHostDelegate* GetTtsDispatcherHostDelegate();
+
   // Getters for common objects.
   virtual net::NetLog* GetNetLog();