4088cd083d
For symmetry with Dart_ThreadExitCallback. Can be used by an embedder to change thread priority or attach native resources to the thread. TEST=ci Change-Id: Ic8eaba7204d0be42db26523b62cbfac3ecb7151f Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/227661 Reviewed-by: Siva Annamalai <asiva@google.com> Commit-Queue: Ryan Macnak <rmacnak@google.com>