linux aura: Show the drag-image when available.

ui/views/widget/widget.h

 // Copyright (c) 2012 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_VIEWS_WIDGET_WIDGET_H_
 #define UI_VIEWS_WIDGET_WIDGET_H_
 
 #include <set>
 #include <stack>
 #include <vector>
@@ skipping 122 matching lines @@
       TYPE_PANEL,       // Always on top window managed by PanelManager.
                         // Widgets of TYPE_PANEL will have a NonClientView.
       TYPE_WINDOW_FRAMELESS,
                         // An undecorated Window.
       TYPE_CONTROL,     // A control, like a button.
       TYPE_POPUP,       // An undecorated Window, with transient properties.
       TYPE_MENU,        // An undecorated Window, with transient properties
                         // specialized to menus.
       TYPE_TOOLTIP,
       TYPE_BUBBLE,
+      TYPE_DRAG,        // An undecorated Window, used during a drag-and-drop to
+                        // show the drag image.
     };
 
     enum WindowOpacity {
       // Infer fully opaque or not. For WinAura, top-level windows that are not
       // of TYPE_WINDOW are translucent so that they can be made to fade in. In
       // all other cases, windows are fully opaque.
       INFER_OPACITY,
       // Fully opaque.
       OPAQUE_WINDOW,
       // Possibly translucent/transparent.
@@ skipping 736 matching lines @@
   // True when window movement via mouse interaction with the frame should be
   // disabled.
   bool movement_disabled_;
 
   DISALLOW_COPY_AND_ASSIGN(Widget);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_WIDGET_H_