Extract the code of showing a dragging window on another display from PhantomWindowController.

ash/shell_window_ids.h

 // 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.
 
 #ifndef ASH_SHELL_WINDOW_IDS_H_
 #define ASH_SHELL_WINDOW_IDS_H_
 
 // Declarations of ids of special shell windows.
 
 namespace ash {
@@ skipping 75 matching lines @@
 const int kShellWindowId_DragImageAndTooltipContainer = 18;
 
 // The container for bubbles briefly overlaid onscreen to show settings changes
 // (volume, brightness, etc.).
 const int kShellWindowId_SettingBubbleContainer = 19;
 
 // The container for special components overlaid onscreen, such as the
 // region selector for partial screenshots.
 const int kShellWindowId_OverlayContainer = 20;
 
-// ID of the window created by PhantomWindowController.
+// ID of the window created by PhantomWindowController or DragWindowController.
 const int kShellWindowId_PhantomWindow = 21;
 
 // The topmost container, used for power off animation.
 const int kShellWindowId_PowerButtonAnimationContainer = 22;
 
 }  // namespace internal
 
 }  // namespace ash
 
 
 #endif  // ASH_SHELL_WINDOW_IDS_H_