Add support for constrained windows on os x, based on Avi's GTMWindowSheetController.

chrome/browser/tab_contents/constrained_window.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef CHROME_BROWSER_TAB_CONTENTS_CONSTRAINED_WINDOW_H_
 #define CHROME_BROWSER_TAB_CONTENTS_CONSTRAINED_WINDOW_H_
 
 #include "chrome/common/page_transition_types.h"
 #include "webkit/glue/window_open_disposition.h"
 
 // The different platform specific subclasses use different delegates for their
 // dialogs.
 #if defined(OS_WIN)
 namespace views {
 class WindowDelegate;
 }
 typedef views::WindowDelegate ConstrainedWindowDelegate;
 #elif defined(OS_LINUX)
 class ConstrainedWindowGtkDelegate;
 typedef ConstrainedWindowGtkDelegate ConstrainedWindowDelegate;
 #elif defined(OS_MACOSX)
-// TODO(port): Change this type when Mac gets ConstrainedWindows. It is here
-// only to make things compile. There is no user or consumer of this type.
-typedef void* ConstrainedWindowDelegate;
+class ConstrainedWindowMacDelegate;
+typedef ConstrainedWindowMacDelegate ConstrainedWindowDelegate;
 #endif
 
 class TabContents;
 
 ///////////////////////////////////////////////////////////////////////////////
 // ConstrainedWindow
 //
 //  This interface represents a window that is constrained to a TabContents'
 //  bounds.
 //
 class ConstrainedWindow {
  public:
   // Create a Constrained Window that contains a platform specific client
   // area. Typical uses include the HTTP Basic Auth prompt. The caller must
   // provide a delegate to describe the content area and to respond to events.
   static ConstrainedWindow* CreateConstrainedDialog(
       TabContents* owner,
       ConstrainedWindowDelegate* delegate);
 
   // Closes the Constrained Window.
   virtual void CloseConstrainedWindow() = 0;
 };
 
 #endif  // CHROME_BROWSER_TAB_CONTENTS_CONSTRAINED_WINDOW_H_