Allow specification of the version file for download_shell_binary to use.

mojo/public/tools/download_shell_binary.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 os
 import subprocess
 import sys
 import tempfile
 import zipfile
 
 BINARY_FOR_PLATFORM = {
     "linux-x64" : "mojo_shell",
     "android-arm" : "MojoShell.apk"
 }
 
 if not sys.platform.startswith("linux"):
   print "Not supported for your platform"
   sys.exit(0)
 
 CURRENT_PATH = os.path.dirname(os.path.realpath(__file__))
 sys.path.insert(0, os.path.join(CURRENT_PATH, "pylib"))
 import gs
 
 PREBUILT_FILE_PATH = os.path.join(CURRENT_PATH, "prebuilt", "shell")
 
 
-def download(tools_directory):
+def download(tools_directory, version_file):
   stamp_path = os.path.join(PREBUILT_FILE_PATH, "VERSION")
 
-  version_path = os.path.join(CURRENT_PATH, "../VERSION")
+  version_path = os.path.join(CURRENT_PATH, version_file)
   with open(version_path) as version_file:
     version = version_file.read().strip()
 
   try:
     with open(stamp_path) as stamp_file:
       current_version = stamp_file.read().strip()
       if current_version == version:
         return 0  # Already have the right version.
   except IOError:
     pass  # If the stamp file does not exist we need to download new binaries.
@@ skipping 31 matching lines @@
   parser = argparse.ArgumentParser(description="Download mojo_shell binaries "
                                    "from google storage")
   parser.add_argument("--tools-directory",
                       dest="tools_directory",
                       metavar="<tools-directory>",
                       type=str,
                       required=True,
                       help="Path to the directory containing "
                            "find_depot_tools.py, specified as a relative path "
                            "from the location of this file.")
+  parser.add_argument("--version-file",
+                      dest="version_file",
+                      metavar="<version-file>",
+                      type=str,
+                      default="../VERSION",
+                      help="Path to the file containing the version of the "
+                           "shell to be fetched, specified as a relative path "
+                           "from the location of this file (default: "
+                           "%(default)s).")
   args = parser.parse_args()
-  return download(args.tools_directory)
+  return download(args.tools_directory, args.version_file)
 
 if __name__ == "__main__":
   sys.exit(main())