Otherwise files containing these characters can be created on the file system,
making it harder to get rid of those files.

TEST=none
BUG=none

Review URL: http://codereview.chromium.org/4127014

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@64782 0039d316-1c4b-4281-b951-d872f2087c98