Fixed guestview sizing bug that resulted in incorrect <webview> sizing on the signin page.

extensions/renderer/resources/guest_view/guest_view_container.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.
 
 // This module implements the shared functionality for different guestview
 // containers, such as web_view, app_view, etc.
 
 var DocumentNatives = requireNative('document_natives');
 var GuestView = require('guestView').GuestView;
 var GuestViewInternalNatives = requireNative('guest_view_internal');
@@ skipping 97 matching lines @@
     }
     this.guest.attach(this.internalInstanceId,
                       this.viewInstanceId,
                       this.buildParams());
   }
 };
 
 GuestViewContainer.prototype.buildParams = function() {
   var params = this.buildContainerParams();
   params['instanceId'] = this.viewInstanceId;
-  params['elementWidth'] = parseInt(this.element.offsetWidth);
-  params['elementHeight'] = parseInt(this.element.offsetHeight);
+  var elementRect = this.element.getBoundingClientRect();
+  params['elementWidth'] = parseInt(elementRect.width);
+  params['elementHeight'] = parseInt(elementRect.height);
   return params;
 };
 
 // Implemented by the specific view type, if needed.
 GuestViewContainer.prototype.buildContainerParams = function() { return {}; };
 GuestViewContainer.prototype.handleAttributeMutation = function() {};
 GuestViewContainer.prototype.onElementAttached = function() {};
 GuestViewContainer.prototype.onElementDetached = function() {
   this.guest.destroy();
 };
@@ skipping 86 matching lines @@
   // Delete the callbacks so developers cannot call them and produce unexpected
   // behavior.
   delete proto.createdCallback;
   delete proto.attachedCallback;
   delete proto.detachedCallback;
   delete proto.attributeChangedCallback;
 }
 
 // Exports.
 exports.GuestViewContainer = GuestViewContainer;