Defer compositor context creation to the thread.

cc/test/layer_tree_pixel_test.cc

Index: cc/test/layer_tree_pixel_test.cc
diff --git a/cc/test/layer_tree_pixel_test.cc b/cc/test/layer_tree_pixel_test.cc
index db48d9734a3c8487c18e6a638ffb9d8ff24881df..72c97477ce1518c17d16c7d1c3abc8a4d8da184c 100644
--- a/cc/test/layer_tree_pixel_test.cc
+++ b/cc/test/layer_tree_pixel_test.cc
@@ -54,10 +54,10 @@ std::unique_ptr<OutputSurface> LayerTreePixelTest::CreateOutputSurface() {
     }
     case PIXEL_TEST_GL: {
       bool flipped_output_surface = false;
-      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 = base::WrapUnique(
           new PixelTestOutputSurface(std::move(compositor), std::move(worker),
                                      flipped_output_surface, nullptr));