This cleans up some of the iteration logic.

BUG=angleproject:2151

Change-Id: I8d80a8d732ee808babbb4859290b648b4fa67b4d
Reviewed-on: https://chromium-review.googlesource.com/673138
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>