Remove implementation of Panels on OSes other than ChromeOS.

chrome/browser/ui/panels/stacked_panel_drag_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 CHROME_BROWSER_UI_PANELS_STACKED_PANEL_DRAG_HANDLER_H_
-#define CHROME_BROWSER_UI_PANELS_STACKED_PANEL_DRAG_HANDLER_H_
-
-#include "base/macros.h"
-
-class Panel;
-namespace gfx {
-class Point;
-}
-
-// Handles all the drags to unstacked free-floating panels.
-class StackedPanelDragHandler {
- public:
-  static void HandleDrag(Panel* panel,
-                         const gfx::Point& target_position,
-                         bool in_orginal_collection);
-
-  static void FinalizeDrag(Panel* panel);
-
- private:
-  DISALLOW_IMPLICIT_CONSTRUCTORS(StackedPanelDragHandler);
-};
-
-#endif  // CHROME_BROWSER_UI_PANELS_STACKED_PANEL_DRAG_HANDLER_H_