Original attempt: https://codereview.chromium.org/1660943002

Now adds depot_tools at the end of PATH to avoid issues with python
on Windows.

TBR=jochen

BUG=437264

Review URL: https://codereview.chromium.org/1661953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@298562 0039d316-1c4b-4281-b951-d872f2087c98