Add locking to all mutable variables of the CL objects in the front end and pass-through back end to make them thread-safe. This fixes a crash in a multi-threaded CTS test. Bug: angleproject:6015 Change-Id: I1d6471c851217639411c434c82acd32d14035291 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2967468 Commit-Queue: John Plate <jplate@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>
