Introduce cc StructTraits unit tests

cc/ipc/traits_test_service.mojom

Index: cc/ipc/traits_test_service.mojom
diff --git a/cc/ipc/traits_test_service.mojom b/cc/ipc/traits_test_service.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..fce582c34aedffb15fcb376b1d70fb95e3111d17
--- /dev/null
+++ b/cc/ipc/traits_test_service.mojom
@@ -0,0 +1,13 @@
+// Copyright 2016 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.
+
+module cc.mojom;
+
+import "cc/ipc/render_pass_id.mojom";
+import "cc/ipc/surface_id.mojom";
+
+interface TraitsTestService {
+  EchoRenderPassId(RenderPassId r) => (RenderPassId pass);
+  EchoSurfaceId(SurfaceId s) => (SurfaceId pass);
+};