Have shelldb and skydb automatically download assets for you

sky/tools/shelldb

 #!/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.
 
 from skypy.skyserver import SkyServer
 import argparse
 import json
 import logging
 import os
@@ skipping 114 matching lines @@
         pids['sky_server_port'])
     url = SkyServer.url_for_path(remote_sky_server_port,
         pids['sky_server_root'], args.url_or_path)
     return _convert_to_sky_url(url)
 
 
 def dev_packages_root(build_dir):
     return os.path.join(build_dir, 'gen', 'dart-pkg', 'packages')
 
 
+def ensure_assets_are_downloaded(build_dir):
+    sky_pkg_dir = os.path.join(build_dir, 'gen', 'dart-pkg', 'sky')
+    sky_pkg_lib_dir = os.path.join(sky_pkg_dir, 'lib')
+    sky_icons_dir = \
+        os.path.join(sky_pkg_lib_dir, 'assets', 'material-design-icons')
+    if not os.path.isdir(sky_icons_dir):
+        logging.info('NOTE: sky/assets/material-design-icons missing, '
+                     'Running `download_material_design_icons` for you.')
+        subprocess.check_call(
+            [os.path.join(sky_pkg_lib_dir, 'download_material_design_icons')])
+
+
 class StartSky(object):
     def add_subparser(self, subparsers):
         start_parser = subparsers.add_parser('start',
-            help='launch SKyShell.apk on the device')
+            help='launch SkyShell.apk on the device')
         start_parser.add_argument('build_dir', type=str)
         start_parser.add_argument('url_or_path', nargs='?', type=str,
             default=DEFAULT_URL)
         start_parser.add_argument('--no_install', action="store_false",
             default=True, dest="install",
             help="Don't install SkyDemo.apk before starting")
         start_parser.set_defaults(func=self.run)
 
     def _server_root_for_url(self, url_or_path):
         path = os.path.abspath(url_or_path)
@@ skipping 13 matching lines @@
         server_root = self._server_root_for_url(args.url_or_path)
         sky_server = SkyServer(SKY_SERVER_PORT, configuration, server_root, packages_root)
         return sky_server
 
     def run(self, args, pids):
         apk_path = os.path.join(args.build_dir, 'apks', APK_NAME)
         if not os.path.exists(apk_path):
             print "'%s' does not exist?" % apk_path
             return 2
 
+        ensure_assets_are_downloaded(args.build_dir)
+
         packages_root = dev_packages_root(args.build_dir)
         sky_server = self._sky_server_for_args(args, packages_root)
         pids['sky_server_pid'] = sky_server.start()
         pids['sky_server_port'] = sky_server.port
         pids['sky_server_root'] = sky_server.root
 
         pids['build_dir'] = os.path.abspath(args.build_dir)
 
         if args.install:
             # -r to replace an existing apk, -d to allow version downgrade.
@@ skipping 152 matching lines @@
         args = parser.parse_args()
         pids = Pids.read_from(PID_FILE_PATH, PID_FILE_KEYS)
         exit_code = args.func(args, pids)
         # We could do this with an at-exit handler instead?
         pids.write_to(PID_FILE_PATH)
         sys.exit(exit_code)
 
 
 if __name__ == '__main__':
     SkyShellRunner().main()