Isolate spawning cleanup.
Isolate spawning cleanup.

Backed out `ReceivePort` experiments.  For now NOT adding custom error and exit handlers actually gets us behavior that's pretty close to what we had before moving to isolates.  (Exceptions are propagated, stack traces printed and error codes properly set.)

R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org//1374083004 .

dart-lang/analyzer_cli,googlearchive/analyzer_cli,googlearchive/analyzer_cli,dart-lang/analyzer_cli