Attempt to fix the MSan failure on chromium bots struct BlockMemberInfo was not tightly packed. This CL makes it packed. Bug: b/296433003 Change-Id: I38da3e463cf304028236e651b6b4e334ce9220e2 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4851063 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Charlie Lao <cclao@google.com>