Implement the rest of the PPAPI examples in the GN build.

ppapi/examples/gles2_spinning_cube/BUILD.gn

Index: ppapi/examples/gles2_spinning_cube/BUILD.gn
diff --git a/ppapi/examples/audio/BUILD.gn b/ppapi/examples/gles2_spinning_cube/BUILD.gn
similarity index 57%
copy from ppapi/examples/audio/BUILD.gn
copy to ppapi/examples/gles2_spinning_cube/BUILD.gn
index f1243d68bbba082d4b7194729ad0d2cc5993220f..26d1ecfb3b5053e0f3031754d40ea58457588a55 100644
--- a/ppapi/examples/audio/BUILD.gn
+++ b/ppapi/examples/gles2_spinning_cube/BUILD.gn
@@ -1,15 +1,18 @@
 # 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.
+# found in the LICENSE file.
 
 import("//ppapi/examples/ppapi_example.gni")
 
-ppapi_example("audio") {
-  output_name = "ppapi_example_audio"
+ppapi_example("gles2_spinning_cube") {
+  output_name = "ppapi_example_gles2_spinning_cube"
   sources = [
-    "audio.cc",
+    "gles2_spinning_cube.cc",
+    "spinning_cube.cc",
+    "spinning_cube.h",
   ]
   deps = [
     "//ppapi/cpp",
+    "//ppapi/lib/gl/gles2",
   ]
 }