GN rules for everything in //mojo

mojo/examples/sample_app/BUILD.gn

 # Copyright 2014 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/system.gni")
 
 # GYP version: mojo/mojo_examples.gypi:mojo_sample_app
 shared_library("sample_app") {
   output_name = "mojo_sample_app"
 
+  sources = [
+    "gles2_client_impl.cc",
+    "gles2_client_impl.h",
+    "sample_app.cc",
+  ]
+
   deps = [
+    ":spinning_cube",
     "//mojo/public/cpp/application:standalone",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/utility",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/interfaces/native_viewport",
   ] + mojo_system_for_shared_library + mojo_gles2_for_shared_library
+}
 
+source_set("spinning_cube") {
   sources = [
-    "gles2_client_impl.cc",
-    "gles2_client_impl.h",
-    "sample_app.cc",
     "spinning_cube.cc",
     "spinning_cube.h"
   ]
+
+  deps = [
+    "//base",
+  ] + mojo_gles2_for_shared_library
 }