Enable AutoResize for Constrained Web Dialogs for Mac.

chrome/browser/ui/cocoa/extensions/extension_install_dialog_controller.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.
 
 #import "chrome/browser/ui/cocoa/extensions/extension_install_dialog_controller.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 37 matching lines @@
             navigator:show_params->GetParentWebContents()
              delegate:this
                prompt:prompt]);
 
   base::scoped_nsobject<NSWindow> window([[ConstrainedWindowCustomWindow alloc]
       initWithContentRect:[[view_controller_ view] bounds]]);
   [[window contentView] addSubview:[view_controller_ view]];
 
   base::scoped_nsobject<CustomConstrainedWindowSheet> sheet(
       [[CustomConstrainedWindowSheet alloc] initWithCustomWindow:window]);
-  constrained_window_.reset(new ConstrainedWindowMac(
+  constrained_window_.reset(CreateAndShowWebModalDialogMac(
       this, show_params->GetParentWebContents(), sheet));
 
   std::string event_name = ExperienceSamplingEvent::kExtensionInstallDialog;
   event_name.append(ExtensionInstallPrompt::PromptTypeToString(prompt->type()));
   sampling_event_ = ExperienceSamplingEvent::Create(event_name);
 }
 
 ExtensionInstallDialogController::~ExtensionInstallDialogController() {
 }
 
@@ skipping 18 matching lines @@
   if (delegate_)
     delegate_->InstallUIAbort(false);
   base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
 // static
 ExtensionInstallPrompt::ShowDialogCallback
 ExtensionInstallPrompt::GetDefaultShowDialogCallback() {
   return base::Bind(&ShowExtensionInstallDialogImpl);
 }