Attach panel while dragging to bring it in front of other panels.

ash/wm/toplevel_window_event_handler.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_WM_TOPLEVEL_WINDOW_EVENT_HANDLER_H_
 #define ASH_WM_TOPLEVEL_WINDOW_EVENT_HANDLER_H_
 
 #include <set>
 
 #include "ash/ash_export.h"
@@ skipping 19 matching lines @@
 class WindowResizer;
 
 class ASH_EXPORT ToplevelWindowEventHandler
     : public ui::EventHandler,
       public aura::client::WindowMoveClient,
       public DisplayController::Observer {
  public:
   explicit ToplevelWindowEventHandler(aura::Window* owner);
   virtual ~ToplevelWindowEventHandler();
 
+  aura::Window* owner() const { return owner_; }

[sky, 2013/03/18 16:17:47]

const aura::Window* owner() const
If you need a non-const version add that too, but it should then be non-const on
both, eg:
aura::Window* owner() { ...

[flackr, 2013/03/20 01:59:32]

Done.

+
   // Overridden from ui::EventHandler:
   virtual void OnKeyEvent(ui::KeyEvent* event) OVERRIDE;
   virtual void OnMouseEvent(ui::MouseEvent* event) OVERRIDE;
   virtual void OnGestureEvent(ui::GestureEvent* event) OVERRIDE;
 
   // Overridden form aura::client::WindowMoveClient:
   virtual aura::client::WindowMoveResult RunMoveLoop(
       aura::Window* source,
       const gfx::Vector2d& drag_offset,
       aura::client::WindowMoveSource move_source) OVERRIDE;
@@ skipping 28 matching lines @@
   // Return value is returned by OnMouseEvent() above.
   void HandleMouseMoved(aura::Window* target, ui::LocatedEvent* event);
 
   // Called for mouse exits to hide window resize shadows.
   // Return value is returned by OnMouseEvent() above.
   void HandleMouseExited(aura::Window* target, ui::LocatedEvent* event);
 
   // Invoked from ScopedWindowResizer if the window is destroyed.
   void ResizerWindowDestroyed();
 
+  // The container which this event handler is handling events on.
+  aura::Window* owner_;
+
   // Are we running a nested message loop from RunMoveLoop().
   bool in_move_loop_;
 
   // Was the move operation cancelled? Used only when the nested loop
   // is used to move a window.
   bool move_cancelled_;
 
   // Is a window move/resize in progress because of gesture events?
   bool in_gesture_drag_;
 
@@ skipping 10 matching lines @@
   // Used to track if this object is deleted while running a nested message
   // loop. If non-null the destructor sets this to true.
   bool* destroyed_;
 
   DISALLOW_COPY_AND_ASSIGN(ToplevelWindowEventHandler);
 };
 
 }  // namespace aura
 
 #endif  // ASH_WM_TOPLEVEL_WINDOW_EVENT_HANDLER_H_