Add a virtualenv-based python bootstrapping service to infra.

run.py

-#!/usr/bin/env python
+#!ENV/bin/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.
 
 """Wrapper for `python -m` to make running tools simpler.
 
 A tool is defined as a python module with a __main__.py file. This latter file
 is run by the present script.
 
 In particular, allows gclient to change directories when running hooks for
 infra.
 """
 
 assert __name__ == '__main__'
 
 import argparse
 import os
 import runpy
 import shlex
 import sys
 import textwrap
 
-from infra.ext import argcomplete
+
+ROOT = os.path.dirname(os.path.abspath(__file__))
+
+if os.path.abspath(sys.prefix) != os.path.join(ROOT, 'ENV'):
+  print 'You must use the virtualenv in ENV for scripts in the infra repo.'
+  print 'Please run this as `./ENV/bin/python run.py`. If you do not have an'
+  print 'ENV directory, please make one with `gclient runhooks`.'
+  sys.exit(1)
+
+
+import argcomplete
 
 
 def main(args):
   os.chdir(os.path.dirname(os.path.abspath(__file__)))
 
   # Impersonate the argcomplete 'protocol'
   completing = os.getenv('_ARGCOMPLETE') == '1'
   if completing:
     assert not args
     line = os.getenv('COMP_LINE')
@@ skipping 34 matching lines @@
     argparse.ArgumentParser.parse_args = new_parse_args
   else:
     # remove the module from sys.argv
     del sys.argv[1]
 
   runpy.run_module(args[0], run_name='__main__', alter_sys=True)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))