Defer compositor context creation to the thread.

cc/test/pixel_test.cc

Index: cc/test/pixel_test.cc
diff --git a/cc/test/pixel_test.cc b/cc/test/pixel_test.cc
index 8faa02f529b236f0781974706db0fdb00687e982..03db0d99788750f167b9841d1f7e1cbcd90b1c1f 100644
--- a/cc/test/pixel_test.cc
+++ b/cc/test/pixel_test.cc
@@ -124,10 +124,10 @@ void PixelTest::SetUpGLRenderer(bool use_skia_gpu_backend,
                                 bool flipped_output_surface) {
   enable_pixel_output_.reset(new gfx::DisableNullDrawGLBindings);
 
-  scoped_refptr<TestInProcessContextProvider> compositor(
-      new TestInProcessContextProvider(nullptr));
   scoped_refptr<TestInProcessContextProvider> worker(
-      new TestInProcessContextProvider(compositor.get()));
+      new TestInProcessContextProvider(nullptr));
+  std::unique_ptr<TestInProcessContextProvider::Factory> compositor(
+      new TestInProcessContextProvider::Factory(worker.get()));
   output_surface_.reset(
       new PixelTestOutputSurface(std::move(compositor), std::move(worker),
                                  flipped_output_surface, nullptr));