Add support for (de)serializing LayerTreeHost.

cc/trees/layer_tree_host_unittest_serialization.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "cc/trees/layer_tree_host.h"
+
+#include "cc/test/layer_tree_test.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cc {
+namespace {
+
+// These tests deal with serialization.
+class LayerTreeHostSerializationTest : public LayerTreeTest {
+ protected:
+  void SetupTree() override { LayerTreeTest::SetupTree(); }
+};
+
+class LayerTreeHostDumbSerializationTest
+    : public LayerTreeHostSerializationTest {
+ public:
+  void BeginTest() override {}
+  void AfterTest() override {}
+};
+
+TEST_F(LayerTreeHostDumbSerializationTest, FooBar) {
+  EXPECT_TRUE(true);
+}
+
+}  // namespace
+}  // namespace cc