GitLab

A 0 mask resource means we don't use a mask, it's a valid value. Don't iterate
over it, because we never want to send 0 to the parent, nor do we want to look
up 0 in the child->parent map.

BUG=None

Review URL: https://codereview.chromium.org/14167007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194689 0039d316-1c4b-4281-b951-d872f2087c98