Add `gclient root` command which outputs the current solution's root.

gclient.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Meta checkout manager supporting both Subversion and GIT."""
 # Files
 #   .gclient      : Current client configuration, written by 'config' command.
 #                   Format is a Python script defining 'solutions', a list whose
 #                   entries each are maps binding the strings "name" and "url"
@@ skipping 1806 matching lines @@
     jobs_arg, args = args[:1], args[1:]
   elif re.match(r'(-j|--jobs)$', args[0]):
     jobs_arg, args = args[:2], args[2:]
 
   return CMDrecurse(
       parser,
       jobs_arg + ['--ignore', '--prepend-dir', '--no-progress', '--scm=git',
                   'git', 'grep', '--null', '--color=Always'] + args)
 
 
+def CMDroot(parser, args):
+  """Outputs the solution root (or current dir if there isn't one)."""
+  (options, args) = parser.parse_args(args)
+  client = GClient.LoadCurrentConfig(options)
+  if client:
+    print(os.path.abspath(client.root_dir))
+  else:
+    print(os.path.abspath('.'))
+
+
 @subcommand.usage('[url] [safesync url]')
 def CMDconfig(parser, args):
   """Creates a .gclient file in the current directory.
 
   This specifies the configuration for further commands. After update/sync,
   top-level DEPS files in each module are read to determine dependent
   modules to operate on as well. If optional [url] parameter is
   provided, then configuration is read from a specified Subversion server
   URL.
   """
@@ skipping 462 matching lines @@
 
 
 if '__main__' == __name__:
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)
 
 # vim: ts=2:sw=2:tw=80:et: