Make pending memory allocation type atomic * This is to prevent TSAN failures due to data race in setPendingMemoryAlloc(). Bug: b/262029018 Change-Id: I5f2f13ecbe762102692bb910a5baa5b25fa42abe Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4115479 Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com> Reviewed-by: Yuxin Hu <yuxinhu@google.com>