- allow the percent sign ('%')
- disallow characters from Windows blacklist https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx#naming_conventions

BUG=467152

Review URL: https://codereview.chromium.org/1035193002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@294591 0039d316-1c4b-4281-b951-d872f2087c98