Make sure WindowObservers are removed from window before destruction

ash/wm/system_modal_container_layout_manager_unittest.cc

 // 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.
 
 #include "ash/wm/system_modal_container_layout_manager.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 110 matching lines @@
 class TransientWindowObserver : public aura::WindowObserver {
  public:
   TransientWindowObserver() : destroyed_(false) {}
   virtual ~TransientWindowObserver() {}
 
   bool destroyed() const { return destroyed_; }
 
   // Overridden from aura::WindowObserver:
   virtual void OnWindowDestroyed(aura::Window* window) OVERRIDE {
     destroyed_ = true;
+    aura::WindowObserver::OnWindowDestroyed(window);
   }
 
  private:
   bool destroyed_;
 
   DISALLOW_COPY_AND_ASSIGN(TransientWindowObserver);
 };
 
 }  // namespace
 
@@ skipping 345 matching lines @@
 
   // No more modal screen.
   modal1->Hide();
   TestWindow::CloseTestWindow(modal1.release());
   EXPECT_FALSE(AllRootWindowsHaveModalBackgrounds());
   EXPECT_TRUE(wm::IsActiveWindow(normal.get()));
 }
 
 }  // namespace test
 }  // namespace ash