mus/views: Fix creating gfx::Display in high-dpi.

ui/aura/test/aura_test_helper.cc

 // Copyright (c) 2012 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/test/aura_test_helper.h"
 
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "ui/aura/client/default_capture_client.h"
 #include "ui/aura/client/focus_client.h"
@@ skipping 51 matching lines @@
   // Unit tests generally don't want to query the system, rather use the state
   // from RootWindow.
   EnvTestHelper env_helper(Env::GetInstance());
   env_helper.SetInputStateLookup(nullptr);
   env_helper.ResetEventState();
 
   ui::InitializeInputMethodForTesting();
 
   gfx::Size host_size(800, 600);
   test_screen_.reset(TestScreen::Create(host_size));
-  gfx::Screen::SetScreenInstance(test_screen_.get());
+  if (!gfx::Screen::GetScreen())
+    gfx::Screen::SetScreenInstance(test_screen_.get());
   host_.reset(test_screen_->CreateHostForPrimaryDisplay());

[sky, 2016/04/20 14:40:10]

If there is a screen will creating host_ at a different size cause problems?

[sadrul, 2016/04/20 14:53:17]

Not sure; the trybots seem happy. But changed this so the TestScreen instance is
created using the existing Screen instance's display size. That should make sure
the WindowTreeHost is created at the size of the primary Display instance.

 
   focus_client_.reset(new TestFocusClient);
   client::SetFocusClient(root_window(), focus_client_.get());
   stacking_client_.reset(new TestWindowTreeClient(root_window()));
   capture_client_.reset(new client::DefaultCaptureClient(root_window()));
 
   root_window()->Show();
   // Ensure width != height so tests won't confuse them.
   host()->SetBounds(gfx::Rect(host_size));
 }
@@ skipping 21 matching lines @@
 
 void AuraTestHelper::RunAllPendingInMessageLoop() {
   // TODO(jbates) crbug.com/134753 Find quitters of this RunLoop and have them
   //              use run_loop.QuitClosure().
   base::RunLoop run_loop;
   run_loop.RunUntilIdle();
 }
 
 }  // namespace test
 }  // namespace aura