As seen in glGetTexLevelParameteriv from gl.xml.

Bug: angleproject:5645
Change-Id: I1d8445f2178632b0edb0652e63984b31a1e34c48
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2718043Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>