Fix crash if root window goes away (most likely from multi-mon).

BUG=145570
TEST=none
R=xiyuan@chromium.org


Review URL: https://chromiumcodereview.appspot.com/10920095

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@155012 0039d316-1c4b-4281-b951-d872f2087c98

ui/views/controls/menu/display_change_listener_aura.cc

@@ -24,6 +24,7 @@ class AuraDisplayChangeListener
   virtual void OnWindowBoundsChanged(aura::Window* window,
                                      const gfx::Rect& old_bounds,
                                      const gfx::Rect& new_bounds) OVERRIDE;
+  virtual void OnWindowDestroying(aura::Window* window) OVERRIDE;
 
  private:
   MenuRunner* menu_runner_;
@@ -52,6 +53,12 @@ void AuraDisplayChangeListener::OnWindowBoundsChanged(
   menu_runner_->Cancel();
 }
 
+void AuraDisplayChangeListener::OnWindowDestroying(aura::Window* window) {
+  DCHECK_EQ(window, root_window_);
+  root_window_->RemoveObserver(this);
+  root_window_ = NULL;
+}
+
 // static
 DisplayChangeListener* DisplayChangeListener::Create(Widget* widget,
                                                      MenuRunner* runner) {