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

content/renderer/render_frame_impl.h

Index: content/renderer/render_frame_impl.h
diff --git a/content/renderer/render_frame_impl.h b/content/renderer/render_frame_impl.h
index dd652ef93d2f9ec6187e01d24974593185c4a7ad..2ad0e342cc1b571d7d1abdc88b6802243532829e 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -61,6 +61,10 @@ class CONTENT_EXPORT RenderFrameImpl
   virtual void willClose(WebKit::WebFrame* frame);
   virtual void didChangeName(WebKit::WebFrame* frame,
                              const WebKit::WebString& name);
+  virtual void didMatchCSS(
+      WebKit::WebFrame* frame,
+      const WebKit::WebVector<WebKit::WebString>& newlyMatchingSelectors,
+      const WebKit::WebVector<WebKit::WebString>& stoppedMatchingSelectors);
   virtual void loadURLExternally(WebKit::WebFrame* frame,
                                  const WebKit::WebURLRequest& request,
                                  WebKit::WebNavigationPolicy policy);