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

chrome/renderer/extensions/extension_helper.cc

 // 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.
 
 #include "chrome/renderer/extensions/extension_helper.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/json/json_string_value_serializer.h"
@@ skipping 212 matching lines @@
   // This could be called before DidCreateDataSource, in which case the frame
   // won't be in the map.
   SchedulerMap::iterator i = g_schedulers.Get().find(frame);
   if (i == g_schedulers.Get().end())
     return;
 
   delete i->second;
   g_schedulers.Get().erase(i);
 }
 
+void ExtensionHelper::DidMatchCSS(
+    WebKit::WebFrame* frame,
+    const WebKit::WebVector<WebKit::WebString>& newly_matching_selectors,
+    const WebKit::WebVector<WebKit::WebString>& stopped_matching_selectors) {
+  dispatcher_->DidMatchCSS(
+      frame, newly_matching_selectors, stopped_matching_selectors);
+}
+
 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.
   if (g_schedulers.Get().count(frame))
     return;
 
   g_schedulers.Get()[frame] = new UserScriptScheduler(frame, dispatcher_);
 }
 
 void ExtensionHelper::OnExtensionResponse(int request_id,
@@ skipping 115 matching lines @@
       render_view()->GetWebView()->mainFrame()->mainWorldScriptContext();
   ChromeV8Context* chrome_v8_context =
       dispatcher_->v8_context_set().GetByV8Context(script_context);
   if (!chrome_v8_context)
     return;
   chrome_v8_context->module_system()->CallModuleMethod(
       "app.window", "onAppWindowClosed");
 }
 
 }  // namespace extensions