Hook up ui::Compositor to Display's BeginFrameSource

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 82045a42c43dd06e91333a64afef477faebc24f2..2a314875d458bd514d79b2517242dafa903aabc0 100644
--- a/cc/test/layer_tree_pixel_test.cc
+++ b/cc/test/layer_tree_pixel_test.cc
@@ -48,15 +48,15 @@ scoped_ptr<OutputSurface> LayerTreePixelTest::CreateOutputSurface() {
           new PixelTestSoftwareOutputDevice);
       software_output_device->set_surface_expansion_size(
           surface_expansion_size);
-      output_surface = make_scoped_ptr(
-          new PixelTestOutputSurface(std::move(software_output_device)));
+      output_surface = make_scoped_ptr(new PixelTestOutputSurface(
+          std::move(software_output_device), nullptr));
       break;
     }
     case PIXEL_TEST_GL: {
       bool flipped_output_surface = false;
       output_surface = make_scoped_ptr(new PixelTestOutputSurface(
           new TestInProcessContextProvider, new TestInProcessContextProvider,
-          flipped_output_surface));
+          flipped_output_surface, nullptr));
       break;
     }
   }