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

ash/drag_drop/drag_drop_controller.cc

 // Copyright (c) 2012 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.
 
 #include "ash/drag_drop/drag_drop_controller.h"
 
 #include "ash/drag_drop/drag_image_view.h"
 #include "ash/shell.h"
 #include "base/message_loop.h"
 #include "ui/aura/client/drag_drop_delegate.h"
@@ skipping 113 matching lines @@
     drag_image_->SetScreenPosition(
         event.root_location().Subtract(drag_image_offset_));
   }
 }
 
 void DragDropController::Drop(aura::Window* target,
                               const aura::LocatedEvent& event) {
   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_);
     drag_operation_ = delegate->OnPerformDrop(e);
     if (drag_operation_ == 0)
       StartCanceledAnimation();
     else
       drag_image_.reset();
   } else {
     drag_image_.reset();
@@ skipping 116 matching lines @@
 void DragDropController::Cleanup() {
   if (drag_window_)
     drag_window_->RemoveObserver(this);
   drag_window_ = NULL;
   drag_data_ = NULL;
   drag_drop_in_progress_ = false;
 }
 
 }  // namespace internal
 }  // namespace ash