Simplify calls for scale factor

ui/aura/window_tree_host.cc

 // Copyright (c) 2013 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/window_tree_host.h"
 
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_port.h"
 #include "ui/aura/window_targeter.h"
 #include "ui/aura/window_tree_host_observer.h"
 #include "ui/base/ime/input_method.h"
 #include "ui/base/ime/input_method_factory.h"
+#include "ui/base/layout.h"
 #include "ui/base/view_prop.h"
 #include "ui/compositor/dip_util.h"
 #include "ui/compositor/layer.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/point3_f.h"
 #include "ui/gfx/geometry/point_conversions.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/icc_profile.h"
 
 namespace aura {
 
 const char kWindowTreeHostForAcceleratedWidget[] =
     "__AURA_WINDOW_TREE_HOST_ACCELERATED_WIDGET__";
 
 float GetDeviceScaleFactorFromDisplay(Window* window) {
-  display::Display display =
-      display::Screen::GetScreen()->GetDisplayNearestWindow(window);
-  DCHECK(display.is_valid());
-  return display.device_scale_factor();
+  return ui::GetScaleFactorForNativeView(window);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // WindowTreeHost, public:
 
 WindowTreeHost::~WindowTreeHost() {
   DCHECK(!compositor_) << "compositor must be destroyed before root window";
   if (owned_input_method_) {
     delete input_method_;
     input_method_ = nullptr;
@@ skipping 293 matching lines @@
   client::CursorClient* cursor_client = client::GetCursorClient(window());
   if (cursor_client) {
     const display::Display& display =
         display::Screen::GetScreen()->GetDisplayNearestWindow(window());
     cursor_client->SetDisplay(display);
   }
   dispatcher()->OnCursorMovedToRootLocation(root_location);
 }
 
 }  // namespace aura