Use GLImage's internal_format for LevelInfo

This is to be consistent with GLES2DecoderImpl and RasterDecoderImpl.

Bug: 870116
Change-Id: I07f7cf15db40046a3ada72bf3fa9621b252dd65e
Reviewed-on: https://chromium-review.googlesource.com/c/1297063
Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602153}
2 files changed