aura: Fix a couple of bug (really the same bug at two different places) for drag

ash/drag_drop/drag_drop_controller.cc

Index: ash/drag_drop/drag_drop_controller.cc
diff --git a/ash/drag_drop/drag_drop_controller.cc b/ash/drag_drop/drag_drop_controller.cc
index 5a3f7df11af78d713f00ca394ac9db092a8542c5..c4dff4f22d5586e1dd59f625f714cd3f80901dcc 100644
--- a/ash/drag_drop/drag_drop_controller.cc
+++ b/ash/drag_drop/drag_drop_controller.cc
@@ -131,10 +131,13 @@ void DragDropController::Drop(aura::Window* target,
   Shell::GetRootWindow()->SetCursor(ui::kCursorPointer);
   aura::client::DragDropDelegate* delegate = NULL;
 
-  // |drag_window_| can be NULL if we have just started the drag and have not
-  // received any DragUpdates, or, if the |drag_window_| gets destroyed during
-  // a drag/drop. Otherwise, target should be equal to the |drag_window_|.
-  DCHECK(target == drag_window_ || !drag_window_);
+  // We must guarantee that a target gets a OnDragEntered before Drop. WebKit
+  // depends on not getting a Drop without DragEnter. This behavior is
+  // consistent with drag/drop on other platforms.
+  if (target != drag_window_)
+    DragUpdate(target, event);
+  DCHECK(target == drag_window_);
+
   if ((delegate = aura::client::GetDragDropDelegate(target))) {
     aura::DropTargetEvent e(
         *drag_data_, event.location(), event.root_location(), drag_operation_);