Fix style inconsistency in packed enum json. Bug: angleproject:2574 Bug: angleproject:2169 Change-Id: I33387bd47979cda7d5239c7128252f860c721a3b Reviewed-on: https://chromium-review.googlesource.com/1067113 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>