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

ash/wm/toplevel_window_event_handler.h

Index: ash/wm/toplevel_window_event_handler.h
diff --git a/ash/wm/toplevel_window_event_handler.h b/ash/wm/toplevel_window_event_handler.h
index 16b4032b2743e3d5882414cd37a2ae7b6f35809c..7376ff7ba4bb41e740b709fc0a08f0211c8dddd9 100644
--- a/ash/wm/toplevel_window_event_handler.h
+++ b/ash/wm/toplevel_window_event_handler.h
@@ -9,6 +9,7 @@
 
 #include "ash/ash_export.h"
 #include "ash/display/display_controller.h"
+#include "ash/wm/window_resizer_owner.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
@@ -32,7 +33,8 @@ class WindowResizer;
 class ASH_EXPORT ToplevelWindowEventHandler
     : public ui::EventHandler,
       public aura::client::WindowMoveClient,
-      public DisplayController::Observer {
+      public DisplayController::Observer,
+      public WindowResizerOwner {
  public:
   explicit ToplevelWindowEventHandler(aura::Window* owner);
   virtual ~ToplevelWindowEventHandler();
@@ -49,9 +51,14 @@ class ASH_EXPORT ToplevelWindowEventHandler
       aura::client::WindowMoveSource move_source) OVERRIDE;
   virtual void EndMoveLoop() OVERRIDE;
 
-  // Overridden form ash::DisplayController::Observer:
+  // Overridden from ash::DisplayController::Observer:
   virtual void OnDisplayConfigurationChanging() OVERRIDE;
 
+  // Overridden from ash::WindowResizerOwner:
+  virtual void PassResizer(WindowResizerOwner* new_owner) OVERRIDE;
+  virtual void AcceptResizer(WindowResizer* resizer,
+                             bool in_gesture_drag) OVERRIDE;
+
  private:
   class ScopedWindowResizer;