Cancel drag if display configuration changes.

ash/display/display_controller.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_DISPLAY_DISPLAY_CONTROLLER_H_
 #define ASH_DISPLAY_DISPLAY_CONTROLLER_H_
 
 #include <map>
 #include <vector>
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
+#include "base/observer_list.h"
 #include "ui/aura/display_observer.h"
 #include "ui/aura/display_manager.h"
 
 namespace aura {
 class Display;
 class RootWindow;
 }
 
 namespace base {
 class Value;
@@ skipping 30 matching lines @@
 
   // The offset of the position of the secondary display.  The offset is
   // based on the top/left edge of the primary display.
   int offset;
 };
 
 // DisplayController owns and maintains RootWindows for each attached
 // display, keeping them in sync with display configuration changes.
 class ASH_EXPORT DisplayController : public aura::DisplayObserver {
  public:
+  class ASH_EXPORT Observer {
+   public:
+    // Invoked when the display configuration change is requested,
+    // but before the change is applied to aura/ash.
+    virtual void OnDisplayConfigurationChanging() = 0;
+
+   protected:
+    virtual ~Observer() {}
+  };
+
   DisplayController();
   virtual ~DisplayController();
 
   // Initializes primary display.
   void InitPrimaryDisplay();
 
   // Initialize secondary displays.
   void InitSecondaryDisplays();
 
+  // Add/Remove observers.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
   // Returns the root window for primary display.
   aura::RootWindow* GetPrimaryRootWindow();
 
   // Returns the root window for |display_id|.
   aura::RootWindow* GetRootWindowForDisplayId(int64 id);
 
   // Closes all child windows in the all root windows.
   void CloseChildWindows();
 
   // Returns all root windows. In non extended desktop mode, this
@@ skipping 21 matching lines @@
   virtual void OnDisplayAdded(const gfx::Display& display) OVERRIDE;
   virtual void OnDisplayRemoved(const gfx::Display& display) OVERRIDE;
 
  private:
   // Creates a root window for |display| and stores it in the |root_windows_|
   // map.
   aura::RootWindow* AddRootWindowForDisplay(const gfx::Display& display);
 
   void UpdateDisplayBoundsForLayout();
 
+  void NotifyDisplayConfigurationChanging();
+
   // The mapping from display ID to its root window.
   std::map<int64, aura::RootWindow*> root_windows_;
 
   // The default display layout.
   DisplayLayout default_display_layout_;
 
   // Per-device display layout.
   std::map<std::string, DisplayLayout> secondary_layouts_;
 
+  ObserverList<Observer> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(DisplayController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DISPLAY_DISPLAY_CONTROLLER_H_