Support dragging panels to stack and snap.

chrome/browser/ui/panels/native_panel.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_NATIVE_PANEL_H_
 #define CHROME_BROWSER_UI_PANELS_NATIVE_PANEL_H_
 
 #include "chrome/browser/ui/panels/panel.h"
 #include "ui/gfx/native_widget_types.h"
 
@@ skipping 60 matching lines @@
   // Gets or sets whether the panel window is always on top.
   virtual bool IsPanelAlwaysOnTop() const = 0;
   virtual void SetPanelAlwaysOnTop(bool on_top) = 0;
 
   // Enables resizing by dragging edges/corners.
   virtual void EnableResizeByMouse(bool enable) = 0;
 
   // Updates the visibility of the minimize and restore buttons.
   virtual void UpdatePanelMinimizeRestoreButtonVisibility() = 0;
 
+  // Updates the panel stacking property due to joining or leaving a stack.
+  virtual void UpdatePanelStackingProperty() = 0;
+
   // Create testing interface for native panel. (Keep this last to separate
   // it from regular API.)
   virtual NativePanelTesting* CreateNativePanelTesting() = 0;
 };
 
 // A NativePanel utility interface used for accessing elements of the
 // native panel used only by test automation.
 class NativePanelTesting {
  public:
   virtual ~NativePanelTesting() {}
@@ skipping 23 matching lines @@
   // Verifies, on a deepest possible level, if the native panel is really
   // showing a correct app icon (taskbar icon).
   virtual bool VerifyAppIcon() const = 0;
 
   virtual bool IsWindowSizeKnown() const = 0;
   virtual bool IsAnimatingBounds() const = 0;
   virtual bool IsButtonVisible(panel::TitlebarButtonType button_type) const = 0;
 };
 
 #endif  // CHROME_BROWSER_UI_PANELS_NATIVE_PANEL_H_