Remove external begin frame source parameter and settings

cc/layers/texture_layer_unittest.cc

Index: cc/layers/texture_layer_unittest.cc
diff --git a/cc/layers/texture_layer_unittest.cc b/cc/layers/texture_layer_unittest.cc
index 0583eab19789f5fa723d46be6af2353af87241e3..072e464cda9b43f33f5e3e2051e02f230f2ddd87 100644
--- a/cc/layers/texture_layer_unittest.cc
+++ b/cc/layers/texture_layer_unittest.cc
@@ -91,7 +91,7 @@ class MockLayerTreeHost : public LayerTreeHostInProcess {
   explicit MockLayerTreeHost(LayerTreeHostInProcess::InitParams* params)
       : LayerTreeHostInProcess(params, CompositorMode::SINGLE_THREADED) {
     InitializeSingleThreaded(&single_thread_client_,
-                             base::ThreadTaskRunnerHandle::Get(), nullptr);
+                             base::ThreadTaskRunnerHandle::Get());
   }
 
   StubLayerTreeHostSingleThreadClient single_thread_client_;