We have to place these classes into a platform namespace to avoid
conflicts with vm/lockers.h.
To avoid changes to files in bin we simply change bin/lockers.h
to introduce bin::{Monitor,Mutex}Locker aliases for
platform::{Monitor,Mutex}Locker.
TEST=ci
R=kustermann@google.com
Change-Id: I975f24a8499ea85d0ba887180a81287fcf4101bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/405460
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>
Vyacheslav Egorov