Add some simple HTMLViewer apptests.

mojo/services/html_viewer/public/interfaces/BUILD.gn

Index: mojo/services/html_viewer/public/interfaces/BUILD.gn
diff --git a/third_party/mojo_services/src/geometry/public/interfaces/BUILD.gn b/mojo/services/html_viewer/public/interfaces/BUILD.gn
similarity index 62%
copy from third_party/mojo_services/src/geometry/public/interfaces/BUILD.gn
copy to mojo/services/html_viewer/public/interfaces/BUILD.gn
index 4896addc10245963f89e7f975c9084d9eeb2c07f..5657884498d0e1361b5ab268da3527a2f53b6050 100644
--- a/third_party/mojo_services/src/geometry/public/interfaces/BUILD.gn
+++ b/mojo/services/html_viewer/public/interfaces/BUILD.gn
@@ -1,12 +1,12 @@
-# Copyright 2014 The Chromium Authors. All rights reserved.
+# 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.
 
-import("../../../mojo_sdk_root.gni")
+import("//build/module_args/mojo.gni")
 import("$mojo_sdk_root/mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
-    "geometry.mojom",
+    "html_viewer.mojom",
   ]
-}
+}