Remove PrepareForShutdown

ash/display/mouse_cursor_event_filter.cc

Index: ash/display/mouse_cursor_event_filter.cc
diff --git a/ash/display/mouse_cursor_event_filter.cc b/ash/display/mouse_cursor_event_filter.cc
index 3710d73c94af21dc1f352249c597dbc1d36ec99f..a91fc645a1301bb1d83e3f6ad53c32f6fff5e747 100644
--- a/ash/display/mouse_cursor_event_filter.cc
+++ b/ash/display/mouse_cursor_event_filter.cc
@@ -8,6 +8,7 @@
 #include "ash/display/display_controller.h"
 #include "ash/display/display_manager.h"
 #include "ash/display/shared_display_edge_indicator.h"
+#include "ash/root_window_controller.h"
 #include "ash/screen_util.h"
 #include "ash/shell.h"
 #include "ash/wm/coordinate_conversion.h"
@@ -75,8 +76,16 @@ void MouseCursorEventFilter::HideSharedEdgeIndicator() {
 }
 
 void MouseCursorEventFilter::OnMouseEvent(ui::MouseEvent* event) {
+  aura::Window* target = static_cast<aura::Window*>(event->target());
+  RootWindowController* rwc = GetRootWindowController(target->GetRootWindow());
+  // The root window controller is removed during the shutting down
+  // RootWindow, so don't process events futher.
+  if (!rwc) {
+    event->StopPropagation();
+    return;
+  }
+
   if (event->type() == ui::ET_MOUSE_PRESSED) {
-    aura::Window* target = static_cast<aura::Window*>(event->target());
     scale_when_drag_started_ = ui::GetDeviceScaleFactor(target->layer());
   } else if (event->type() == ui::ET_MOUSE_RELEASED) {
     scale_when_drag_started_ = 1.0f;
@@ -96,7 +105,6 @@ void MouseCursorEventFilter::OnMouseEvent(ui::MouseEvent* event) {
   }
 
   gfx::Point point_in_screen(event->location());
-  aura::Window* target = static_cast<aura::Window*>(event->target());
   wm::ConvertPointToScreen(target, &point_in_screen);
   if (WarpMouseCursorIfNecessary(target->GetRootWindow(), point_in_screen))
     event->StopPropagation();