Disable context menu on signin page in the embedded flow

chrome/browser/resources/gaia_auth/main.js

 // 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.
 
 /**
  * Authenticator class wraps the communications between Gaia and its host.
  */
 function Authenticator() {
 }
 
@@ skipping 150 matching lines @@
     var gaiaFrame = $('gaia-frame');
     gaiaFrame.partition = this.partitionId_;
     gaiaFrame.src = this.initialFrameUrl_;
     if (this.inlineMode_) {
       gaiaFrame.addEventListener(
           'loadstop', this.onWebviewLoadstop_.bind(this, gaiaFrame));
       gaiaFrame.addEventListener(
           'newwindow', this.onWebviewNewWindow_.bind(this, gaiaFrame));
     }
     if (this.constrained_) {
+      var preventContextMenu = 'document.addEventListener("contextmenu", ' +
+                               'function(e) {e.preventDefault();})';
+      gaiaFrame.executeScript({code: preventContextMenu});
       gaiaFrame.request.onCompleted.addListener(
           this.onWebviewRequestCompleted_.bind(this),
           {urls: ['<all_urls>'], types: ['main_frame']},
           ['responseHeaders']);
     }
   },
 
   completeLogin: function(username, password) {
     var msg = {
       'method': 'completeLogin',
@@ skipping 153 matching lines @@
     } else if (msg.method == 'redirectToSignin' &&
                this.isParentMessage_(e)) {
       $('gaia-frame').src = this.constructInitialFrameUrl_();
     } else {
        console.error('Authenticator.onMessage: unknown message + origin!?');
     }
   }
 };
 
 Authenticator.getInstance().initialize();