Introduce separate client and init path for single-threaded cc

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 d793473e8559970aacdd7dd810eaa1ee29203356..5acc9c57b08ec7ecce9ef67f66b77b78941ca2c6 100644
--- a/cc/layers/texture_layer_unittest.cc
+++ b/cc/layers/texture_layer_unittest.cc
@@ -43,9 +43,9 @@ namespace {
 
 class MockLayerTreeHost : public LayerTreeHost {
  public:
-  explicit MockLayerTreeHost(LayerTreeHostClient* client)
+  explicit MockLayerTreeHost(FakeLayerTreeHostClient* client)
       : LayerTreeHost(client, NULL, LayerTreeSettings()) {
-    Initialize(NULL);
+    InitializeSingleThreaded(client);
   }
 
   MOCK_METHOD0(AcquireLayerTextures, void());