Also enables a test in LineLoopTest that validates this case.

Bug: angleproject:2473

Change-Id: Icb4c5735c11be40cdeceaa051f5a5cef33fd22c6
Reviewed-on: https://chromium-review.googlesource.com/1011669
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>