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

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 1b56512d376508eed8ae10942a520ebf3b37b455..7beca6095ca154ea565ec5b84d71a2224b7a639d 100644
--- a/ui/aura/test/aura_test_helper.cc
+++ b/ui/aura/test/aura_test_helper.cc
@@ -64,7 +64,8 @@ void AuraTestHelper::SetUp(ui::ContextFactory* context_factory) {
 
   ui::InitializeInputMethodForTesting();
 
-  test_screen_.reset(TestScreen::Create());
+  gfx::Size host_size(800, 600);
+  test_screen_.reset(TestScreen::Create(host_size));
   gfx::Screen::SetScreenInstance(gfx::SCREEN_TYPE_NATIVE, test_screen_.get());
   host_.reset(test_screen_->CreateHostForPrimaryDisplay());
 
@@ -79,7 +80,7 @@ void AuraTestHelper::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));
 }
 
 void AuraTestHelper::TearDown() {