Support running dartdevc in worker mode in an isolate.
Support running dartdevc in worker mode in an isolate.

Change-Id: If3e596cfc5ad1fa956e73e9d44053be5d1f24338
Reviewed-on: https://dart-review.googlesource.com/c/80202
Commit-Queue: David Morgan <c99f6ead588e81ca6564615e2a62f86df17041f2@google.com>
Reviewed-by: Jenny Messerly <6285f43aa2dd0931180012d62b847adf2c37a418@google.com>

dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk