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

cc/test/test_hooks.h

Index: cc/test/test_hooks.h
diff --git a/cc/test/test_hooks.h b/cc/test/test_hooks.h
index 61f6f82a7a71253ba6e5c5681c337a20e80771b9..3c947b70f25baebdf32aeb3cc399f7ceee6891c6 100644
--- a/cc/test/test_hooks.h
+++ b/cc/test/test_hooks.h
@@ -113,7 +113,11 @@ class TestHooks : public AnimationDelegate {
                                std::unique_ptr<AnimationCurve> curve) override {
   }
 
+  // OutputSurface indirections to the LayerTreeTest, that can be further
+  // overridden.
   virtual void RequestNewCompositorFrameSink() = 0;
+  virtual std::unique_ptr<OutputSurface> CreateDisplayOutputSurfaceOnThread(
+      scoped_refptr<ContextProvider> compositor_context_provider) = 0;
 };
 
 }  // namespace cc