[Mac] "Refactor" DraggableButton into a mixin and impl.

chrome/chrome_browser.gypi

 # Copyright (c) 2011 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'dependencies': [
@@ skipping 2427 matching lines @@
         'browser/ui/cocoa/download/download_shelf_view.mm',
         'browser/ui/cocoa/download/download_show_all_button.h',
         'browser/ui/cocoa/download/download_show_all_button.mm',
         'browser/ui/cocoa/download/download_show_all_cell.h',
         'browser/ui/cocoa/download/download_show_all_cell.mm',
         'browser/ui/cocoa/download/download_started_animation_mac.mm',
         'browser/ui/cocoa/download/download_util_mac.h',
         'browser/ui/cocoa/download/download_util_mac.mm',
         'browser/ui/cocoa/draggable_button.h',
         'browser/ui/cocoa/draggable_button.mm',
+        'browser/ui/cocoa/draggable_button_mixin.h',
+        'browser/ui/cocoa/draggable_button_mixin.mm',
         'browser/ui/cocoa/drag_util.h',
         'browser/ui/cocoa/drag_util.mm',
         'browser/ui/cocoa/encoding_menu_controller_delegate_mac.h',
         'browser/ui/cocoa/encoding_menu_controller_delegate_mac.mm',
         'browser/ui/cocoa/event_utils.h',
         'browser/ui/cocoa/event_utils.mm',
         'browser/ui/cocoa/extensions/browser_action_button.h',
         'browser/ui/cocoa/extensions/browser_action_button.mm',
         'browser/ui/cocoa/extensions/browser_actions_container_view.h',
         'browser/ui/cocoa/extensions/browser_actions_container_view.mm',
@@ skipping 2551 matching lines @@
               # weak imports in dependents, who still must #include
               # closure_blocks_leopard_compat.h to get weak imports.
               'type': 'none',
             }],
           ],
         },
       ],
     }],
   ],
 }