Implement ui/gfx/geometry StructTraits unit tests

ui/gfx/mojo/BUILD.gn

 # 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.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("mojo") {
   sources = [
     "transform.mojom",
   ]
 }
+
+mojom("test_interfaces") {
+  sources = [
+    "traits_test_service.mojom",
+  ]
+
+  public_deps = [
+    ":mojo",
+  ]
+}