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

ui/aura/test/aura_test_helper.cc

Index: ui/aura/test/aura_test_helper.cc
diff --git a/ui/aura/test/aura_test_helper.cc b/ui/aura/test/aura_test_helper.cc
index 2d679e59f184c7f2248e374f1e65832776bb6b06..6e985387f009265e2885e9844363967fa5ccb7ea 100644
--- a/ui/aura/test/aura_test_helper.cc
+++ b/ui/aura/test/aura_test_helper.cc
@@ -69,7 +69,8 @@ void AuraTestHelper::SetUp(ui::ContextFactory* context_factory) {
 
   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);