First shot at implementing drag&drop for Aura

ui/aura/event.h

Index: ui/aura/event.h
diff --git a/ui/aura/event.h b/ui/aura/event.h
index e01e6c25423d323c098a5f380d7ec9a99c11afd9..5dcb72666b0099601416b7704426210a6a30a10c 100644
--- a/ui/aura/event.h
+++ b/ui/aura/event.h
@@ -10,6 +10,7 @@
 #include "base/event_types.h"
 #include "base/time.h"
 #include "ui/aura/aura_export.h"
+#include "ui/base/dragdrop/os_exchange_data.h"
 #include "ui/base/events.h"
 #include "ui/base/keycodes/keyboard_codes.h"
 #include "ui/gfx/point.h"
@@ -180,6 +181,29 @@ class AURA_EXPORT KeyEvent : public Event {
   uint16 unmodified_character_;
 };
 
+class AURA_EXPORT DropTargetEvent : public LocatedEvent {
+ public:
+  DropTargetEvent(const ui::OSExchangeData& data,
+                  const gfx::Point& location,
+                  int source_operations)
+      : LocatedEvent(ui::ET_DROP_TARGET_EVENT, location, 0),
+        data_(data),
+        source_operations_(source_operations) {
+  }
+
+  const ui::OSExchangeData& data() const { return data_; }
+  int source_operations() const { return source_operations_; }
+
+ private:
+  // Data associated with the drag/drop session.
+  const ui::OSExchangeData& data_;
+
+  // Bitmask of supported ui::DragDropTypes::DragOperation by the source.
+  int source_operations_;
+
+  DISALLOW_COPY_AND_ASSIGN(DropTargetEvent);
+};
+
 }  // namespace aura
 
 #endif  // UI_AURA_EVENT_H_