[Chromoting] Add missing file to webapp's GN build.

remoting/remoting_webapp_files.gypi

 # 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.
 
-# Keep in sync with remoting/webapp/files.gni.
+# `7MM"""Mq.                       `7MM
+#   MM   `MM.                        MM
+#   MM   ,M9  .gP"Ya   ,6"Yb.   ,M""bMM  `7MMpMMMb.pMMMb.  .gP"Ya
+#   MMmmdM9  ,M'   Yb 8)   MM ,AP    MM    MM    MM    MM ,M'   Yb
+#   MM  YM.  8M""""""  ,pm9MM 8MI    MM    MM    MM    MM 8M""""""
+#   MM   `Mb.YM.    , 8M   MM `Mb    MM    MM    MM    MM YM.    ,
+# .JMML. .JMM.`Mbmmd' `Moo9^Yo.`Wbmd"MML..JMML  JMML  JMML.`Mbmmd'
+#
+# Please keep this file in sync with remoting/webapp/files.gni.
 
 {
   'variables': {
 
     # Jscompile proto files.
     # These provide type information for jscompile.
     'remoting_webapp_js_proto_files': [
       'webapp/js_proto/chrome_proto.js',
       'webapp/js_proto/chrome_cast_proto.js',
       'webapp/js_proto/chrome_event_proto.js',
@@ skipping 478 matching lines @@
       '<(remoting_webapp_template_background)',
       '<(remoting_webapp_template_main)',
       '<(remoting_webapp_template_message_window)',
       '<(remoting_webapp_template_wcs_sandbox)',
       '<@(remoting_webapp_template_files)',
       '<@(remoting_webapp_crd_js_files)',
     ],
 
   },
 }