Standardize Screen::GetCursorScreenPoint() on Env::last_mouse_location

ui/views/mus/screen_mus.h

 // Copyright 2016 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.
 
 #ifndef UI_VIEWS_MUS_SCREEN_MUS_H_
 #define UI_VIEWS_MUS_SCREEN_MUS_H_
 
 #include "mojo/public/cpp/bindings/binding.h"
 #include "services/ui/public/interfaces/display_manager.mojom.h"
 #include "ui/display/screen_base.h"
 #include "ui/views/mus/mus_export.h"
 
 namespace service_manager {
 class Connector;
 }
 
 namespace views {
 
 class ScreenMusDelegate;
 
 // Screen implementation backed by ui::mojom::DisplayManager.
 class VIEWS_MUS_EXPORT ScreenMus
     : public display::ScreenBase,
       public NON_EXPORTED_BASE(ui::mojom::DisplayManagerObserver) {
  public:
-  // |delegate| can be nullptr.
   explicit ScreenMus(ScreenMusDelegate* delegate);
   ~ScreenMus() override;
 
   void Init(service_manager::Connector* connector);
 
  private:
   // display::Screen:
   gfx::Point GetCursorScreenPoint() override;
   bool IsWindowUnderCursor(gfx::NativeWindow window) override;
   aura::Window* GetWindowAtScreenPoint(const gfx::Point& point) override;
 
   // ui::mojom::DisplayManager:
   void OnDisplays(std::vector<ui::mojom::WsDisplayPtr> ws_displays,
                   int64_t primary_display_id,
                   int64_t internal_display_id) override;
   void OnDisplaysChanged(
       std::vector<ui::mojom::WsDisplayPtr> ws_displays) override;
   void OnDisplayRemoved(int64_t display_id) override;
   void OnPrimaryDisplayChanged(int64_t primary_display_id) override;
 
-  ScreenMusDelegate* delegate_;  // Can be nullptr.
+  ScreenMusDelegate* delegate_;
   ui::mojom::DisplayManagerPtr display_manager_;
   mojo::Binding<ui::mojom::DisplayManagerObserver>
       display_manager_observer_binding_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenMus);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_SCREEN_MUS_H_