Revert of Simplify mojo_shell since it's now only used for Mandoline.

mojo/tools/android_mojo_shell.py

 #!/usr/bin/env python
 # 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 argparse
 import logging
 import sys
 
 from mopy.config import Config
 from mopy import android
 
+USAGE = ("android_mojo_shell.py "
+         "[--args-for=<mojo-app>] "
+         "[--content-handlers=<handlers>] "
+         "[--enable-external-applications] "
+         "[--disable-cache] "
+         "[--enable-multiprocess] "
+         "[--url-mappings=from1=to1,from2=to2] "
+         "[<mojo-app>] "
+         """
+
+A <mojo-app> is a Mojo URL or a Mojo URL and arguments within quotes.
+Example: mojo_shell "mojo:js_standalone test.js".
+<url-lib-path> is searched for shared libraries named by mojo URLs.
+The value of <handlers> is a comma separated list like:
+text/html,mojo:html_viewer,application/javascript,mojo:js_content_handler
+""")
+
+
 def main():
   logging.basicConfig()
 
-  parser = argparse.ArgumentParser("Helper for running mojo_shell")
+  parser = argparse.ArgumentParser(usage=USAGE)
 
   debug_group = parser.add_mutually_exclusive_group()
   debug_group.add_argument('--debug', help='Debug build (default)',
                            default=True, action='store_true')
   debug_group.add_argument('--release', help='Release build', default=False,
                            dest='debug', action='store_false')
   parser.add_argument('--target-cpu', help='CPU architecture to run for.',
                       choices=['x64', 'x86', 'arm'])
   parser.add_argument('--origin', help='Origin for mojo: URLs.')
   launcher_args, args = parser.parse_known_args()
 
   config = Config(target_os=Config.OS_ANDROID,
                   target_cpu=launcher_args.target_cpu,
                   is_debug=launcher_args.debug)
 
   extra_shell_args = android.PrepareShellRun(config, launcher_args.origin)
   args.extend(extra_shell_args)
 
   android.CleanLogs()
   p = android.ShowLogs()
   android.StartShell(args, sys.stdout, p.terminate)
   return 0
 
 
 if __name__ == "__main__":
   sys.exit(main())