First shot at implementing drag&drop for Aura

ui/aura/client/aura_constants.h

 // 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.
 
 #ifndef UI_AURA_CLIENT_AURA_CONSTANTS_H_
 #define UI_AURA_CLIENT_AURA_CONSTANTS_H_
 #pragma once
 
 #include "ui/aura/aura_export.h"
 
@@ skipping 11 matching lines @@
 // See ui/base/ui_base_types.h for its definition.
 AURA_EXPORT extern const char kShowStateKey[];
 
 // A property key to store tooltip text for a window. The type of the value
 // is |string16*|.
 AURA_EXPORT extern const char kTooltipTextKey[];
 
 // A property key to store the boolean property of window modality.
 AURA_EXPORT extern const char kModalKey[];
 
+// A property key to store the drag and drop client for the desktop. The type of
+// the value is |aura::DragDropClient*|.
+AURA_EXPORT extern const char kDesktopDragDropClientKey[];
+
+// A property key to store the drag and drop delegate for a window. The type of
+// the value is |aura::WindowDragDropDelegate*|.
+AURA_EXPORT extern const char kDragDropDelegateKey[];
 }  // namespace aura
 
 #endif  // UI_AURA_CLIENT_AURA_CONSTANTS_H_