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

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index b886c0c844b352d454739da3f88f95aae6068852..bc8e15021064be26646fd170a01d87c2ea0dd4c8 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -274,6 +274,14 @@ void RenderFrameImpl::didChangeName(WebKit::WebFrame* frame,
                                       UTF16ToUTF8(name)));
 }
 
+void RenderFrameImpl::didMatchCSS(
+    WebKit::WebFrame* frame,
+    const WebKit::WebVector<WebKit::WebString>& newlyMatchingSelectors,
+    const WebKit::WebVector<WebKit::WebString>& stoppedMatchingSelectors) {
+  render_view_->didMatchCSS(
+      frame, newlyMatchingSelectors, stoppedMatchingSelectors);
+}
+
 void RenderFrameImpl::loadURLExternally(WebKit::WebFrame* frame,
                                         const WebKit::WebURLRequest& request,
                                         WebKit::WebNavigationPolicy policy) {