So that if the process dies in the middle, the files are easier to spot and
delete.

R=iannucci@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/19498004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@213081 0039d316-1c4b-4281-b951-d872f2087c98