Regenerate .mojo file if any dependent .dart sources change

mojo/public/tools/dart_snapshotter.py

 #!/usr/bin/env python
 # 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 argparse
 import subprocess
 import sys
 import os
 
 def main():
   parser = argparse.ArgumentParser(description='Snapshots Mojo applications')
   parser.add_argument('executable', type=str)
   parser.add_argument('main', type=str)
   parser.add_argument('--package-root', type=str)
   parser.add_argument('--snapshot', type=str)
+  parser.add_argument('--depfile', type=str)
+  parser.add_argument('--build-output', type=str)
 
   args = parser.parse_args()
   if not os.path.isfile(args.executable):
     print "file not found: " + args.executable
   return subprocess.check_call([
     args.executable,
     args.main,
     '--package-root=%s' % args.package_root,
     '--snapshot=%s' % args.snapshot,
+    '--depfile=%s' % args.depfile,
+    '--build-output=%s' % args.build_output,
   ])
 
 if __name__ == '__main__':
   sys.exit(main())