Use Blink support to watch CSS selectors directly instead of using a MutationObserver.

chrome/renderer/extensions/extension_helper.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_RENDERER_EXTENSIONS_EXTENSION_HELPER_H_
 #define CHROME_RENDERER_EXTENSIONS_EXTENSION_HELPER_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 45 matching lines @@
   Dispatcher* dispatcher() const { return dispatcher_; }
 
  private:
   // RenderViewObserver implementation.
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
   virtual void DidFinishDocumentLoad(WebKit::WebFrame* frame) OVERRIDE;
   virtual void DidFinishLoad(WebKit::WebFrame* frame) OVERRIDE;
   virtual void DidCreateDocumentElement(WebKit::WebFrame* frame) OVERRIDE;
   virtual void DidStartProvisionalLoad(WebKit::WebFrame* frame) OVERRIDE;
   virtual void FrameDetached(WebKit::WebFrame* frame) OVERRIDE;
+  virtual void DidMatchCSS(
+      WebKit::WebFrame* frame,
+      const WebKit::WebVector<WebKit::WebString>& newly_matching_selectors,
+      const WebKit::WebVector<WebKit::WebString>& stopped_matching_selectors)
+      OVERRIDE;
   virtual void DidCreateDataSource(WebKit::WebFrame* frame,
                                    WebKit::WebDataSource* ds) OVERRIDE;
   virtual void DraggableRegionsChanged(WebKit::WebFrame* frame) OVERRIDE;
 
   void OnExtensionResponse(int request_id, bool success,
                            const base::ListValue& response,
                            const std::string& error);
   void OnExtensionMessageInvoke(const std::string& extension_id,
                                 const std::string& module_name,
                                 const std::string& function_name,
@@ skipping 36 matching lines @@
 
   // Id number of browser window which RenderView is attached to.
   int browser_window_id_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionHelper);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_RENDERER_EXTENSIONS_EXTENSION_HELPER_H_