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

chrome/renderer/extensions/extension_helper.cc

Index: chrome/renderer/extensions/extension_helper.cc
diff --git a/chrome/renderer/extensions/extension_helper.cc b/chrome/renderer/extensions/extension_helper.cc
index 041578c42902eb8a9547c5ca1d768640e23ba4fa..5975065059b67c887b3e7d4ee14badacd1ebf41e 100644
--- a/chrome/renderer/extensions/extension_helper.cc
+++ b/chrome/renderer/extensions/extension_helper.cc
@@ -230,6 +230,14 @@ void ExtensionHelper::FrameDetached(WebFrame* frame) {
   g_schedulers.Get().erase(i);
 }
 
+void ExtensionHelper::DidMatchCSS(
+    WebKit::WebFrame* frame,
+    const WebKit::WebVector<WebKit::WebString>& newlyMatchingSelectors,
+    const WebKit::WebVector<WebKit::WebString>& stoppedMatchingSelectors) {
+  dispatcher_->DidMatchCSS(
+      frame, newlyMatchingSelectors, stoppedMatchingSelectors);
+}
+
 void ExtensionHelper::DidCreateDataSource(WebFrame* frame, WebDataSource* ds) {
   // Check first if we created a scheduler for the frame, since this function
   // gets called for navigations within the document.