Fix window/display bounds with multiple windows in mus.

services/ui/display/platform_screen_impl.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 SERVICES_UI_DISPLAY_PLATFORM_SCREEN_IMPL_H_
 #define SERVICES_UI_DISPLAY_PLATFORM_SCREEN_IMPL_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
 #include "services/ui/display/platform_screen.h"
 
 namespace display {
 
 // PlatformScreenImpl provides the necessary functionality to configure all
 // attached physical displays on non-ozone platforms.
 class PlatformScreenImpl : public PlatformScreen {
  public:
   PlatformScreenImpl();
   ~PlatformScreenImpl() override;
 
  private:
   // PlatformScreen.
   void Init() override;
   void ConfigurePhysicalDisplay(
       const PlatformScreen::ConfiguredDisplayCallback& callback) override;
+  int64_t GetPrimaryDisplayId() const override;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformScreenImpl);
 };
 
 }  // namespace display
 
 #endif  // SERVICES_UI_DISPLAY_PLATFORM_SCREEN_IMPL_H_