cac1319768
Allow updating weak handles etc to happen in parallel with work-stealing.
Also make LocalBlockWorklist more symmetric with BlockWorklist.
Cf. 4495c2b30a
TEST=ci
Change-Id: Id58fe16be92028b1aa4dd8f097769b4107f2a3f0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/316043
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>