Update references to the extension messaging APIs to point to the "runtime"

chrome/common/extensions/docs/examples/extensions/proxy_configuration/proxy_form_controller.js

 // Copyright (c) 2011 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.
 
 /**
  * @fileoverview This file implements the ProxyFormController class, which
  * wraps a form element with logic that enables implementation of proxy
  * settings.
  *
  * @author mkwst@google.com (Mike West)
@@ skipping 506 matching lines @@
     chrome.extension.sendRequest({type: 'clearError'});
   },
 
   /**
    * Called in response to setting a regular window's proxy settings: checks
    * for `lastError`, and then sets incognito settings (if they exist).
    *
    * @private
    */
   callbackForRegularSettings_: function() {
-    if (chrome.extension.lastError) {
+    if (chrome.runtime.lastError) {
       this.generateAlert_(chrome.i18n.getMessage('errorSettingRegularProxy'));
       return;
     }
     if (this.config_.incognito) {
       chrome.proxy.settings.set(
           {value: this.config_.incognito, scope: 'incognito_persistent'},
           this.callbackForIncognitoSettings_.bind(this));
     } else {
       ProxyFormController.setPersistedSettings(this.config_);
       this.generateAlert_(chrome.i18n.getMessage('successfullySetProxy'));
     }
   },
 
   /**
    * Called in response to setting an incognito window's proxy settings: checks
    * for `lastError` and sets a success message.
    *
    * @private
    */
   callbackForIncognitoSettings_: function() {
-    if (chrome.extension.lastError) {
+    if (chrome.runtime.lastError) {
       this.generateAlert_(chrome.i18n.getMessage('errorSettingIncognitoProxy'));
       return;
     }
     ProxyFormController.setPersistedSettings(this.config_);
     this.generateAlert_(
         chrome.i18n.getMessage('successfullySetProxy'));
   },
 
   /**
    * Generates an alert overlay inside the proxy's popup, then closes the popup
@@ skipping 225 matching lines @@
       console.error(error);
       // TODO(mkwst): Do something more interesting
       this.generateAlert_(
           chrome.i18n.getMessage(
               error.details ? 'errorProxyDetailedError' : 'errorProxyError',
               [error.error, error.details]),
           false);
     }
   }
 };