We would incorrectly check the storage type after we had redefined it.
Thus we would allow old storages to persist for some cases of 3D
texture. This bug did not affect 2D textures.

See WebGL 2 test: conformance2/misc/views-with-offsets.html

BUG=angleproject:1609

Change-Id: I7a04ff498740bb5d7daf2cee174c336f97a44c01
Reviewed-on: https://chromium-review.googlesource.com/408417Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>