Get drag and drop working for win aura.

ui/views/widget/desktop_aura/desktop_root_window_host_win.h

Index: ui/views/widget/desktop_aura/desktop_root_window_host_win.h
===================================================================
--- ui/views/widget/desktop_aura/desktop_root_window_host_win.h	(revision 171535)
+++ ui/views/widget/desktop_aura/desktop_root_window_host_win.h	(working copy)
@@ -22,6 +22,7 @@
 class DesktopActivationClient;
 class DesktopCursorClient;
 class DesktopDispatcherClient;
+class DesktopDragDropClientWin;
 class HWNDMessageHandler;
 namespace corewm {
 class CompoundEventFilter;
@@ -231,6 +232,8 @@
   // A simple cursor client which just forwards events to the RootWindow.
   scoped_ptr<DesktopCursorClient> cursor_client_;
 
+  scoped_ptr<DesktopDragDropClientWin> drag_drop_client_;
+
   // The RootWindow's CompoundEventFilter.
   views::corewm::CompoundEventFilter* root_window_event_filter_;