Add extension event histogram values for messaging, webRequest, and webview.

extensions/renderer/resources/extension_custom_bindings.js

 // 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.
 
 // Custom binding for the extension API.
 
 var binding = require('binding').Binding.create('extension');
 
 var messaging = require('messaging');
 var runtimeNatives = requireNative('runtime');
 var GetExtensionViews = runtimeNatives.GetExtensionViews;
-var OpenChannelToExtension = runtimeNatives.OpenChannelToExtension;
-var OpenChannelToNativeApp = runtimeNatives.OpenChannelToNativeApp;
 var chrome = requireNative('chrome').GetChrome();
 
 var inIncognitoContext = requireNative('process').InIncognitoContext();
 var sendRequestIsDisabled = requireNative('process').IsSendRequestDisabled();
 var contextType = requireNative('process').GetContextType();
 var manifestVersion = requireNative('process').GetManifestVersion();
 
 // This should match chrome.windows.WINDOW_ID_NONE.
 //
 // We can't use chrome.windows.WINDOW_ID_NONE directly because the
@@ skipping 80 matching lines @@
     };
     if (contextType == 'BLESSED_EXTENSION') {
       extension.onRequestExternal.addListener = function() {
         throw new Error(sendRequestIsDisabled);
       };
     }
   }
 });
 
 exports.binding = binding.generate();