Defer compositor context creation to the thread.

cc/test/pixel_test_output_surface.h

Index: cc/test/pixel_test_output_surface.h
diff --git a/cc/test/pixel_test_output_surface.h b/cc/test/pixel_test_output_surface.h
index 6cd4191adedce7b7eb7b77f905198a3188fa6865..799804851324f9c93008566bd77fa38f5b646101 100644
--- a/cc/test/pixel_test_output_surface.h
+++ b/cc/test/pixel_test_output_surface.h
@@ -14,15 +14,11 @@ class BeginFrameSource;
 class PixelTestOutputSurface : public OutputSurface {
  public:
   explicit PixelTestOutputSurface(
-      scoped_refptr<ContextProvider> context_provider,
+      std::unique_ptr<ContextProvider::Factory> compositor_context_factory,
       scoped_refptr<ContextProvider> worker_context_provider,
       bool flipped_output_surface,
       std::unique_ptr<BeginFrameSource> begin_frame_source);
   explicit PixelTestOutputSurface(
-      scoped_refptr<ContextProvider> context_provider,
-      bool flipped_output_surface,
-      std::unique_ptr<BeginFrameSource> begin_frame_source);
-  explicit PixelTestOutputSurface(
       std::unique_ptr<SoftwareOutputDevice> software_device,
       std::unique_ptr<BeginFrameSource> begin_frame_source);
   ~PixelTestOutputSurface() override;