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

ash/wm/window_resizer_owner.h

Index: ash/wm/window_resizer_owner.h
diff --git a/ash/wm/window_resizer_owner.h b/ash/wm/window_resizer_owner.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4b906b88957a326969c51b990ce04667f45965f
--- /dev/null
+++ b/ash/wm/window_resizer_owner.h
@@ -0,0 +1,26 @@
+// Copyright (c) 2013 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_WINDOW_RESIZER_OWNER_H_
+#define ASH_WM_WINDOW_RESIZER_OWNER_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+class WindowResizer;
+
+class ASH_EXPORT WindowResizerOwner {
+ public:
+  // Pass the owned WindowResizer to a different WindowResizerOwner.
+  virtual void PassResizer(WindowResizerOwner* new_owner) = 0;
+
+  // Accept and take ownership of a passed WindowResizer object.
+  virtual void AcceptResizer(WindowResizer* resizer,
+                             bool in_gesture_drag) = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_WM_WINDOW_RESIZER_OWNER_H_