bd0d029792
In presence of isolate-less mutators, the check for "single mutator"-scenario is not-trivial, acquiring active_mutator_count mutex results in circular mutex dependencies. BUG=https://github.com/dart-lang/sdk/issues/60857 BUG=https://github.com/dart-lang/sdk/issues/60953 TEST=ci Change-Id: I5a12f9b8d4bc54042137012668ed1afee7c7739f Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/435241 Reviewed-by: Ryan Macnak <rmacnak@google.com> Commit-Queue: Alexander Aprelev <aam@google.com>