[Reland] Enable AutoResize for Constrained Web Dialogs for Mac.

chrome/browser/ui/cocoa/extensions/media_galleries_dialog_cocoa.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/extensions/media_galleries_dialog_cocoa.h"
 
 #include <stddef.h>
 
 #include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 84 matching lines @@
   [[alert_ closeButton] setTarget:cocoa_controller_];
   [[alert_ closeButton] setAction:@selector(onCancelButton:)];
 
   InitDialogControls();
 
   // May be NULL during tests.
   if (controller->WebContents()) {
     base::scoped_nsobject<CustomConstrainedWindowSheet> sheet(
         [[CustomConstrainedWindowSheet alloc]
             initWithCustomWindow:[alert_ window]]);
-    window_.reset(new ConstrainedWindowMac(
-        this, controller->WebContents(), sheet));
+    window_ = CreateAndShowWebModalDialogMac(
+        this, controller->WebContents(), sheet);
   }
 }
 
 MediaGalleriesDialogCocoa::~MediaGalleriesDialogCocoa() {
 }
 
 void MediaGalleriesDialogCocoa::AcceptDialogForTesting() {
   OnAcceptClicked();
 }
 
@@ skipping 161 matching lines @@
   return controller_->GetContextMenu(pref_id);
 }
 
 // static
 MediaGalleriesDialog* MediaGalleriesDialog::Create(
     MediaGalleriesDialogController* controller) {
   base::scoped_nsobject<MediaGalleriesCocoaController> cocoa_controller(
       [[MediaGalleriesCocoaController alloc] init]);
   return new MediaGalleriesDialogCocoa(controller, cocoa_controller);
 }