Fix workaround formats not being used when EXT_texture_storage is emulated. This bug showed up on Mac which doesn't support the extension. The internalFormat is correctly translated to the workaround format but the format and type are not. BUG=angleproject:1958 Change-Id: I9b31f0491df1bb623bf59996cbb02d0276b6355c Reviewed-on: https://chromium-review.googlesource.com/488582 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>