Enable AutoResize for Constrained Web Dialogs for Mac.

chrome/browser/ui/cocoa/tab_modal_confirm_dialog_mac.mm

 // 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.
 
 #include "chrome/browser/ui/cocoa/tab_modal_confirm_dialog_mac.h"
 
 #include "base/mac/scoped_nsobject.h"
 #include "chrome/browser/ui/browser_dialogs.h"
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_alert.h"
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.h"
@@ skipping 70 matching lines @@
               keyEquivalent:kKeyEquivalentEscape
                      target:bridge_
                      action:@selector(onCancelButton:)];
   [[alert_ closeButton] setTarget:bridge_];
   [[alert_ closeButton] setAction:@selector(onCancelButton:)];
   [alert_ layout];
 
   base::scoped_nsobject<CustomConstrainedWindowSheet> sheet(
       [[CustomConstrainedWindowSheet alloc]
           initWithCustomWindow:[alert_ window]]);
-  window_.reset(new ConstrainedWindowMac(this, web_contents, sheet));
+  window_.reset(CreateAndShowWebModalDialogMac(this, web_contents, sheet));
   delegate_->set_close_delegate(this);
 }
 
 TabModalConfirmDialogMac::~TabModalConfirmDialogMac() {
 }
 
 void TabModalConfirmDialogMac::AcceptTabModalDialog() {
   delegate_->Accept();
 }
 
@@ skipping 13 matching lines @@
   // If this method should mistakenly be called during Delegate::Close(),
   // prevent a double-delete by moving delegate_ to a stack variable.
   if (!delegate_)
     return;
   scoped_ptr<TabModalConfirmDialogDelegate> delegate(delegate_.Pass());
   // Provide a disposition in case the dialog was closed without accepting or
   // cancelling.
   delegate->Close();
   delete this;
 }