Hook up ui::Compositor to Display's BeginFrameSource

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 9c968bde7260904a7f4396d75272bab4f705ae85..98601553471867b8d94740b978bcee1700e88549 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -124,6 +124,7 @@ class LayerTreeHostImplTest : public testing::Test,
   void DidLoseOutputSurfaceOnImplThread() override {}
   void CommitVSyncParameters(base::TimeTicks timebase,
                              base::TimeDelta interval) override {}
+  void SetBeginFrameSource(BeginFrameSource* source) override {}
   void SetEstimatedParentDrawTime(base::TimeDelta draw_time) override {}
   void DidSwapBuffersOnImplThread() override {}
   void DidSwapBuffersCompleteOnImplThread() override {}