Use more gl::Error in IndexDataManager. BUG=angleproject:2229 Change-Id: I19f7c1600300298e7bc2a1f7dc4215a67053767c Reviewed-on: https://chromium-review.googlesource.com/764674 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>