Adds support for multiple displays to WmTestBase

ash/mus/test/wm_test_screen.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 ASH_MUS_TEST_WM_TEST_SCREEN_H_
-#define ASH_MUS_TEST_WM_TEST_SCREEN_H_
-
-#include "ui/display/screen_base.h"
-
-namespace ash {
-namespace mus {
-
-// Screen implementation used by tests for the windowmanager. Does not talk
-// to mus. Tests must keep the list of Displays in sync manually.
-class WmTestScreen : public display::ScreenBase {
- public:
-  WmTestScreen();
-  ~WmTestScreen() override;
-
- private:
-  // display::ScreenBase:
-  gfx::Point GetCursorScreenPoint() override;
-  bool IsWindowUnderCursor(gfx::NativeWindow window) override;
-
-  DISALLOW_COPY_AND_ASSIGN(WmTestScreen);
-};
-
-}  // namespace mus
-}  // namespace ash
-
-#endif  // ASH_MUS_TEST_WM_TEST_SCREEN_H_