Add a virtualenv-based python bootstrapping service to infra.

infra/ext/__init__.py

-# 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 os
-import sys
-
-# Explicit import paths for sub-projects that don't follow the
-# 'infra/ext/<package>/<package>/' directory layout.
-EXTPACKAGES = {
-    'httplib2': os.path.join('httplib2', 'python' + str(sys.version_info[0])),
-    'pytz': os.path.join('pytz', 'src'),
-    }
-
-
-def _add_ext_dirs_to_path():
-  base = os.path.dirname(os.path.abspath(__file__))
-
-  for d in os.listdir(base):
-    full = os.path.join(base, EXTPACKAGES.get(d, d))
-    if os.path.isdir(full):
-      # TODO(iannucci): look for egg
-      # Needed to support absolute imports in sub-projects (e.g. pytz has
-      # imports like: from pytz.exceptions import AmbiguousTimeError).
-      sys.path.insert(0, full)
-      # Needed to support 'import infra.ext.foo' syntax.
-      __path__.append(full)
-
-_add_ext_dirs_to_path()
-
-# Enough of a hint for pylint / jedi (autocompletion) to find and follow the
-# imports, but doesn't make python import them immediately at runtime.
-#
-# This list should always contain a complete list of all modules in ext.
-if False:
-  import argcomplete
-  import dateutil
-  import httplib2
-  import oauth2client
-  import pytz
-  import requests