Added posix and windows runner scripts for download_from_google_storage.py

Windows bots are having trouble calling download_from_google_storage.py from the
DEPS hooks.  This should allow it to be called as just "download_from_google_storage".

BUG=
R=maruel@chromium.org

Review URL: https://codereview.chromium.org/15395002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@200939 0039d316-1c4b-4281-b951-d872f2087c98

download_from_google_storage

+#!/usr/bin/env bash
+# Copyright (c) 2009 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.
+
+base_dir=$(dirname "$0")
+
+PYTHONDONTWRITEBYTECODE=1 exec python "$base_dir/download_from_google_storage.py" "$@"

download_from_google_storage.bat

+@echo off
+:: 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.
+
+:: This is required with cygwin only.
+PATH=%~dp0;%PATH%
+
+:: Defer control.
+%~dp0python "%~dp0\download_from_google_storage.py" %*