First shot at implementing drag&drop for Aura

ui/aura/desktop.h

Index: ui/aura/desktop.h
diff --git a/ui/aura/desktop.h b/ui/aura/desktop.h
index 7a58b48a67ed35b64d6ba58ad4bbb107aedd0dbc..717981191911baeb9e2f607273e8e010cdfa7c4b 100644
--- a/ui/aura/desktop.h
+++ b/ui/aura/desktop.h
@@ -15,6 +15,7 @@
 #include "ui/aura/cursor.h"
 #include "ui/aura/focus_manager.h"
 #include "ui/aura/window.h"
+#include "ui/base/dragdrop/os_exchange_data.h"
 #include "ui/base/events.h"
 #include "ui/gfx/compositor/compositor.h"
 #include "ui/gfx/compositor/layer_animation_observer.h"
@@ -131,6 +132,9 @@ class AURA_EXPORT Desktop : public ui::CompositorDelegate,
   // Overridden from Window:
   virtual void SetTransform(const ui::Transform& transform) OVERRIDE;
 
+  // Initiates a drag and drop session
+  virtual void StartDragAndDrop(const ui::OSExchangeData& data, int operation);
+
  private:
   // Called whenever the mouse moves, tracks the current |mouse_moved_handler_|,
   // sending exited and entered events as its value changes.
@@ -206,6 +210,8 @@ class AURA_EXPORT Desktop : public ui::CompositorDelegate,
   Window* focused_window_;
   Window* touch_event_handler_;
 
+  bool drag_drop_in_progress_;
+
   DISALLOW_COPY_AND_ASSIGN(Desktop);
 };