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

ash/wm/window_resizer.h

Index: ash/wm/window_resizer.h
diff --git a/ash/wm/window_resizer.h b/ash/wm/window_resizer.h
index bc46df85e31a51b9adb9d2932678303db03eee87..e3c54c253b079289b9d52b6321ec0ce992686e7c 100644
--- a/ash/wm/window_resizer.h
+++ b/ash/wm/window_resizer.h
@@ -16,6 +16,8 @@ class Window;
 
 namespace ash {
 
+class WindowResizerOwner;
+
 // WindowResizer is used by ToplevelWindowEventFilter to handle dragging, moving
 // or resizing a window. All coordinates passed to this are in the parent
 // windows coordinates.
@@ -124,7 +126,9 @@ class ASH_EXPORT WindowResizer {
 
 // Creates a WindowResizer for |window|. This can return a scoped_ptr
 // initialized with NULL if |window| should not be resized nor dragged.
+// If |owner| is not NULL the resizer may pass itself to other resizer owners.
 ASH_EXPORT scoped_ptr<WindowResizer> CreateWindowResizer(
+    WindowResizerOwner* owner,
     aura::Window* window,
     const gfx::Point& point_in_parent,
     int window_component);