Rewrite scoped_ptr<T>(NULL) to use the default ctor in ash/.

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_drop_tracker.h"
 #include "ash/drag_drop/drag_image_view.h"
 #include "ash/shell.h"
 #include "ash/wm/coordinate_conversion.h"
@@ skipping 121 matching lines @@
  private:
   DragDropController* drag_drop_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(DragDropTrackerDelegate);
 };
 
 ////////////////////////////////////////////////////////////////////////////////
 // DragDropController, public:
 
 DragDropController::DragDropController()
-    : drag_image_(NULL),
-      drag_data_(NULL),
+    : drag_data_(NULL),
       drag_operation_(0),
       drag_window_(NULL),
       drag_source_window_(NULL),
       should_block_during_drag_drop_(true),
       drag_drop_window_delegate_(new DragDropTrackerDelegate(this)),
       current_drag_event_source_(ui::DragDropTypes::DRAG_EVENT_SOURCE_MOUSE),
       weak_factory_(this) {
   Shell::GetInstance()->PrependPreTargetHandler(this);
 }
 
@@ skipping 405 matching lines @@
     drag_window_->RemoveObserver(this);
   drag_window_ = NULL;
   drag_data_ = NULL;
   // Cleanup can be called again while deleting DragDropTracker, so use Pass
   // instead of reset to avoid double free.
   drag_drop_tracker_.Pass();
 }
 
 }  // namespace internal
 }  // namespace ash