aura: Allow specifying the size of TestScreen when creating it.

athena/test/athena_test_helper.cc

Index: athena/test/athena_test_helper.cc
diff --git a/athena/test/athena_test_helper.cc b/athena/test/athena_test_helper.cc
index 1b99ea85316ac094590b77efe7c21226ba846f04..2e87d3e600da03d3b6d10f587c57568131221242 100644
--- a/athena/test/athena_test_helper.cc
+++ b/athena/test/athena_test_helper.cc
@@ -56,7 +56,8 @@ void AthenaTestHelper::SetUp(ui::ContextFactory* context_factory) {
 
   ui::InitializeInputMethodForTesting();
 
-  test_screen_.reset(aura::TestScreen::Create());
+  const gfx::Size host_size(800, 600);
+  test_screen_.reset(aura::TestScreen::Create(host_size));
   gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, test_screen_.get());
   host_.reset(test_screen_->CreateHostForPrimaryDisplay());
 
@@ -73,7 +74,7 @@ void AthenaTestHelper::SetUp(ui::ContextFactory* context_factory) {
 
   root_window()->Show();
   // Ensure width != height so tests won't confuse them.
-  host()->SetBounds(gfx::Rect(800, 600));
+  host()->SetBounds(gfx::Rect(host_size));
 
   athena::StartAthena(root_window(),
                       new SampleActivityFactory(),