BrowserPlugin: Simplify guest access

content/public/browser/browser_plugin_guest_manager.cc

 // Copyright 2014 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 "content/public/browser/browser_plugin_guest_manager.h"
 
 #include "base/values.h"
 
 namespace content {
 
+WebContents* BrowserPluginGuestManager::GetGuestByInstanceID(
+    WebContents* embedder_web_contents,
+    int browser_plugin_instance_id) {
+  return NULL;
+}
+
 bool BrowserPluginGuestManager::ForEachGuest(
     WebContents* embedder_web_contents,
     const GuestCallback& callback) {
   return false;
 }
 
 }  // content