Stack panels so that part of them will always be visible.

ash/wm/panel_layout_manager.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 ASH_WM_PANEL_LAYOUT_MANAGER_H_
 #define ASH_WM_PANEL_LAYOUT_MANAGER_H_
 #pragma once
 
 #include <list>
 
 #include "ash/ash_export.h"
 #include "ash/launcher/launcher_icon_observer.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/aura/layout_manager.h"
+#include "ui/aura/window_observer.h"
 
 namespace aura {
 class Window;
 }
 
 namespace gfx {
 class Rect;
 }
 
 namespace ash {
 class Launcher;
 
 namespace internal {
 
 // PanelLayoutManager is responsible for organizing panels within the
 // workspace. It is associated with a specific container window (i.e.
 // kShellWindowId_PanelContainer) and controls the layout of any windows
 // added to that container.
 //
 // The constructor takes a |panel_container| argument which is expected to set
 // its layout manager to this instance, e.g.:
 // panel_container->SetLayoutManager(new PanelLayoutManager(panel_container));
 
 class ASH_EXPORT PanelLayoutManager : public aura::LayoutManager,
-                                      public ash::LauncherIconObserver {
+                                      public ash::LauncherIconObserver,
+                                      public aura::WindowObserver {
  public:
   explicit PanelLayoutManager(aura::Window* panel_container);
   virtual ~PanelLayoutManager();
 
   void StartDragging(aura::Window* panel);
   void FinishDragging();
 
   void ToggleMinimize(aura::Window* panel);
 
   void SetLauncher(ash::Launcher* launcher);
 
   // Overridden from aura::LayoutManager:
   virtual void OnWindowResized() OVERRIDE;
   virtual void OnWindowAddedToLayout(aura::Window* child) OVERRIDE;
   virtual void OnWillRemoveWindowFromLayout(aura::Window* child) OVERRIDE;
   virtual void OnWindowRemovedFromLayout(aura::Window* child) OVERRIDE;
   virtual void OnChildWindowVisibilityChanged(aura::Window* child,
                                               bool visibile) OVERRIDE;
   virtual void SetChildBounds(aura::Window* child,
                               const gfx::Rect& requested_bounds) OVERRIDE;
 
-  // Overriden from ash::LauncherIconObserver
+  // Overridden from ash::LauncherIconObserver
   virtual void OnLauncherIconPositionsChanged() OVERRIDE;
 
+  // Overridden from aura::WindowObserver
+  virtual void OnWindowPropertyChanged(
+      aura::Window* window, const void* key, intptr_t old) OVERRIDE;
+
  private:
   typedef std::list<aura::Window*> PanelList;
 
   // Called whenever the panel layout might change.
   void Relayout();
 
+  // Called whenever the panel stacking order needs to be updated (e.g. focus
+  // changes or a panel is moved).
+  void UpdateStacking(aura::Window* active_panel);
+
   // Parent window associated with this layout manager.
   aura::Window* panel_container_;
   // Protect against recursive calls to Relayout().
   bool in_layout_;
   // Ordered list of unowned pointers to panel windows.
   PanelList panel_windows_;
-
+  // The panel being dragged.
   aura::Window* dragged_panel_;
-
+  // The launcher we are observing for launcher icon changes.
   Launcher* launcher_;
+  // The last active panel. Used to maintain stacking even if no panels are
+  // currently focused.
+  aura::Window* last_active_panel_;
 
   DISALLOW_COPY_AND_ASSIGN(PanelLayoutManager);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_WM_PANEL_LAYOUT_MANAGER_H_