Enable touch-initiated drag-drop work on Windows

ui/base/dragdrop/drag_source_win.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_BASE_DRAGDROP_DRAG_SOURCE_WIN_H_
 #define UI_BASE_DRAGDROP_DRAG_SOURCE_WIN_H_
 
 #include <objidl.h>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
+#include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/base/ui_export.h"
 
 namespace ui {
 
 // A base IDropSource implementation. Handles notifications sent by an active
 // drag-drop operation as the user mouses over other drop targets on their
 // system. This object tells Windows whether or not the drag should continue,
 // and supplies the appropriate cursors.
 class UI_EXPORT DragSourceWin
     : public IDropSource,
       public base::RefCountedThreadSafe<DragSourceWin> {
  public:
   DragSourceWin();
+  explicit DragSourceWin(DragDropTypes::DragEventSource event_source);
   virtual ~DragSourceWin() {}
 
   // Stop the drag operation at the next chance we get.  This doesn't
   // synchronously stop the drag (since Windows is controlling that),
   // but lets us tell Windows to cancel the drag the next chance we get.
   void CancelDrag() {
     cancel_drag_ = true;
   }
 
   // IDropSource implementation:
   HRESULT __stdcall QueryContinueDrag(BOOL escape_pressed, DWORD key_state);
   HRESULT __stdcall GiveFeedback(DWORD effect);
 
   // IUnknown implementation:
   HRESULT __stdcall QueryInterface(const IID& iid, void** object);
   ULONG __stdcall AddRef();
   ULONG __stdcall Release();
 
  protected:
   virtual void OnDragSourceCancel() {}
   virtual void OnDragSourceDrop() {}
   virtual void OnDragSourceMove() {}
 
  private:
   // Set to true if we want to cancel the drag operation.
   bool cancel_drag_;
 
+  // Indicate the drag initiator, mouse or touch.
+  const DragDropTypes::DragEventSource event_source_;
+
   DISALLOW_COPY_AND_ASSIGN(DragSourceWin);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DRAGDROP_DRAG_SOURCE_WIN_H_