First shot at implementing drag&drop for Aura

ui/aura/client/aura_constants.h

Index: ui/aura/client/aura_constants.h
diff --git a/ui/aura/client/aura_constants.h b/ui/aura/client/aura_constants.h
index c2065638533708e118717b4ec876a1524ceaf6ee..80204f34408c2f279dbb8fc354fd1e387e101ad6 100644
--- a/ui/aura/client/aura_constants.h
+++ b/ui/aura/client/aura_constants.h
@@ -26,6 +26,14 @@ AURA_EXPORT extern const char kShowStateKey[];
 // is |string16*|.
 AURA_EXPORT extern const char kTooltipTextKey[];
 
+// A property key to store the drag and drop client for the desktop. The type of
+// the value is |aura::DragDropClient*|.
+AURA_EXPORT extern const char kDesktopDragDropClientKey[];
+
+// A property key to store the drag and drop delegate for a window. The type of
+// the value is |aura::WindowDragDropDelegate*|.
+AURA_EXPORT extern const char kDragDropDelegateKey[];
+
 }  // namespace aura
 
 #endif  // UI_AURA_CLIENT_AURA_CONSTANTS_H_