First shot at implementing drag&drop for Aura

ui/aura/aura.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 29 matching lines @@
         'event_filter.cc',
         'event_filter.h',
         'focus_manager.h',
         'layout_manager.cc',
         'layout_manager.h',
         'screen_aura.cc',
         'screen_aura.h',
         'window.cc',
         'window.h',
         'window_delegate.h',
+        'window_drag_drop_delegate.h',
         'window_observer.h',
         'window_types.h',
       ],
     },
     {
       'target_name': 'test_support_aura',
       'type': 'static_library',
       'dependencies': [
         '../../skia/skia.gyp:skia',
         '../../testing/gtest.gyp:gtest',
@@ skipping 75 matching lines @@
       'conditions': [
         ['OS=="linux"', {
           'dependencies': [
             '<(DEPTH)/third_party/mesa/mesa.gyp:osmesa',
           ],
         }],
       ],
     },
   ],
 }