Fix window/display bounds with multiple windows in mus.

services/ui/display/platform_screen_impl.cc

 // 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.
 
 #include "services/ui/display/platform_screen_impl.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace display {
 namespace {
 
+const int64_t kDisplayId = 1;
+
 void FixedSizeScreenConfiguration(
     const PlatformScreen::ConfiguredDisplayCallback& callback) {
-  callback.Run(1, gfx::Rect(1024, 768));
+  callback.Run(kDisplayId, gfx::Rect(1024, 768));
 }
 
 }  // namespace
 
 // static
 std::unique_ptr<PlatformScreen> PlatformScreen::Create() {
   return base::WrapUnique(new PlatformScreenImpl);
 }
 
 PlatformScreenImpl::PlatformScreenImpl() {}
 
 PlatformScreenImpl::~PlatformScreenImpl() {}
 
 void PlatformScreenImpl::Init() {}
 
 void PlatformScreenImpl::ConfigurePhysicalDisplay(
     const PlatformScreen::ConfiguredDisplayCallback& callback) {
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE, base::Bind(&FixedSizeScreenConfiguration, callback));
 }
 
+int64_t PlatformScreenImpl::GetPrimaryDisplayId() const {
+  return kDisplayId;
+}
+
 }  // namespace display