Add two demos which exercise the audio server.

examples/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("//build/config/ui.gni")
 
 group("examples") {
   testonly = true
 
   deps = [
     "//examples/apptest",
+    "//examples/audio_play_test",
     "//examples/content_handler_demo",
     "//examples/dart",
     "//examples/echo",
     "//examples/echo_terminal",
     "//examples/embedded_app",
     "//examples/forwarding_content_handler",
     "//examples/ganesh_app",
     "//examples/http_handler",
     "//examples/indirect_service",
     "//examples/keyboard_client",
@@ skipping 39 matching lines @@
   }
 
   if (is_linux && !is_fnl) {
     deps += [ "//examples/python" ]
   }
 
   if (is_linux && !is_asan && !is_fnl) {
     deps += [ "//examples/spinning_cube(//build/toolchain/nacl:newlib_pnacl)" ]
   }
 }