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

chrome/renderer/extensions/dispatcher.h

Index: chrome/renderer/extensions/dispatcher.h
diff --git a/chrome/renderer/extensions/dispatcher.h b/chrome/renderer/extensions/dispatcher.h
index 180007651177f1496c4acef55e6a62cee93379bf..50b54605daae0ab31e9c0f72b299e564e8361579 100644
--- a/chrome/renderer/extensions/dispatcher.h
+++ b/chrome/renderer/extensions/dispatcher.h
@@ -20,6 +20,8 @@
 #include "content/public/renderer/render_process_observer.h"
 #include "extensions/common/event_filter.h"
 #include "extensions/common/features/feature.h"
+#include "third_party/WebKit/public/platform/WebString.h"
+#include "third_party/WebKit/public/platform/WebVector.h"
 #include "v8/include/v8.h"
 
 class ChromeRenderViewTest;
@@ -97,6 +99,11 @@ class Dispatcher : public content::RenderProcessObserver {
 
   void DidCreateDocumentElement(WebKit::WebFrame* frame);
 
+  void DidMatchCSS(
+      WebKit::WebFrame* frame,
+      const WebKit::WebVector<WebKit::WebString>& newlyMatchingSelectors,
+      const WebKit::WebVector<WebKit::WebString>& stoppedMatchingSelectors);
+
   // TODO(mpcomplete): remove. http://crbug.com/100411
   bool IsAdblockWithWebRequestInstalled() const {
     return webrequest_adblock_;