Ignore update cursor messages from blink when the cursor position lies outside our root window

ui/aura/test/test_screen.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 "ui/aura/test/test_screen.h"
 
 #include "base/logging.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
@@ skipping 111 matching lines @@
 
 gfx::Point TestScreen::GetCursorScreenPoint() {
   return Env::GetInstance()->last_mouse_location();
 }
 
 gfx::NativeWindow TestScreen::GetWindowUnderCursor() {
   return GetWindowAtScreenPoint(GetCursorScreenPoint());
 }
 
 gfx::NativeWindow TestScreen::GetWindowAtScreenPoint(const gfx::Point& point) {
+  if (!host_ || !host_->window())
+    return nullptr;
   return host_->window()->GetTopWindowContainingPoint(point);
 }
 
 int TestScreen::GetNumDisplays() const {
   return 1;
 }
 
 std::vector<gfx::Display> TestScreen::GetAllDisplays() const {
   return std::vector<gfx::Display>(1, display_);
 }
@@ skipping 23 matching lines @@
 
 TestScreen::TestScreen(const gfx::Rect& screen_bounds)
     : host_(NULL),
       ui_scale_(1.0f) {
   static int64 synthesized_display_id = 2000;
   display_.set_id(synthesized_display_id++);
   display_.SetScaleAndBounds(1.0f, screen_bounds);
 }
 
 }  // namespace aura