First shot at implementing drag&drop for Aura

ui/aura/client/drag_drop_client.h

Index: ui/aura/client/drag_drop_client.h
diff --git a/ui/aura/client/drag_drop_client.h b/ui/aura/client/drag_drop_client.h
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+++ b/ui/aura/client/drag_drop_client.h
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+// 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_DRAG_DROP_CLIENT_H_
+#define UI_AURA_CLIENT_DRAG_DROP_CLIENT_H_
+#pragma once
+
+#include "ui/aura/aura_export.h"
+#include "ui/aura/event.h"
+
+namespace ui {
+class OSExchangeData;
+}
+
+namespace aura {
+
+class Window;
+
+// An interface implemented by an object that controls a drag and drop session.
+class AURA_EXPORT DragDropClient {
+ public:
+  virtual ~DragDropClient() {}
+
+  // Initiates a drag and drop session
+  virtual void StartDragAndDrop(const ui::OSExchangeData& data,
+                                int operation) = 0;
+
+  // Called when mouse is dragged during a drag and drop.
+  virtual void DragUpdate(aura::Window* target, const MouseEvent& event) = 0;
+
+  // Called when mouse is released during a drag and drop.
+  virtual void Drop(aura::Window* target, const MouseEvent& event) = 0;
+
+  // Called when a drag and drop session is cancelled.
+  virtual void DragCancel() = 0;
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_CLIENT_DRAG_DROP_CLIENT_H_