Make download items drag sources on OS X.

chrome/browser/cocoa/download_item_controller.h

 // Copyright (c) 2009 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 <Cocoa/Cocoa.h>
 
 #include "base/scoped_ptr.h"
 #include "base/time.h"
 
 class BaseDownloadItemModel;
 @class ChromeUILocalizer;
 @class DownloadItemCell;
 class DownloadItem;
+@class DownloadItemButton;
 class DownloadItemMac;
 class DownloadShelfContextMenuMac;
 @class DownloadShelfController;
 @class GTMWidthBasedTweaker;
 
 // A controller class that manages one download item.
 
 @interface DownloadItemController : NSViewController {
  @private
-  IBOutlet NSButton* progressView_;
+  IBOutlet DownloadItemButton* progressView_;
   IBOutlet DownloadItemCell* cell_;
 
   IBOutlet NSMenu* activeDownloadMenu_;
   IBOutlet NSMenu* completeDownloadMenu_;
 
   NSMenu* currentMenu_;  // points to one of the two menus above
 
   // This is shown instead of progressView_ for dangerous downloads.
   IBOutlet NSView* dangerousDownloadView_;
   IBOutlet NSTextField* dangerousDownloadLabel_;
@@ skipping 61 matching lines @@
 
 // Context menu handlers.
 - (IBAction)handleOpen:(id)sender;
 - (IBAction)handleAlwaysOpen:(id)sender;
 - (IBAction)handleReveal:(id)sender;
 - (IBAction)handleCancel:(id)sender;
 - (IBAction)handleTogglePause:(id)sender;
 
 @end