Ensure pls results are secure even without barriers We can't guarantee the client will always use local storage barriers correctly, but we CAN guard local storage passes such that the results are only nondeterministic within predictable constraints. This CL adds a test to ensure local storage is still predictable without barriers, and that no data is random or leaked from other contexts. Bug: angleproject:7279 Bug: angleproject:7398 Change-Id: I70da58c8ba79b09f560315df3df956d1721ff6b9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3654265 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Auto-Submit: Chris Dalton <chris@rive.app> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>