cc: Make OutputSurface entirely live on one thread in tests.

cc/test/layer_tree_test.h

Index: cc/test/layer_tree_test.h
diff --git a/cc/test/layer_tree_test.h b/cc/test/layer_tree_test.h
index 4ee47443f0e8ed952be148798065c62af4f04738..6c58ab765786f2c04433afe6b605b302d31099a4 100644
--- a/cc/test/layer_tree_test.h
+++ b/cc/test/layer_tree_test.h
@@ -152,8 +152,8 @@ class LayerTreeTest : public testing::Test, public TestHooks {
   // CompositorFrameSink. Or override it and create your own OutputSurface to
   // change what type of OutputSurface is used, such as a real OutputSurface for
   // pixel tests or a software-compositing OutputSurface.
-  virtual std::unique_ptr<OutputSurface> CreateDisplayOutputSurface(
-      scoped_refptr<ContextProvider> compositor_context_provider);
+  std::unique_ptr<OutputSurface> CreateDisplayOutputSurfaceOnThread(
+      scoped_refptr<ContextProvider> compositor_context_provider) override;
 
   bool IsRemoteTest() const;