This allows test environments other than `flutter test` to have a hook
into the test exception reporting. Some test environments, for example,
don't just dump error details to the console, but rather require them
to be reported to a separate server.

The new values are not ready for use yet inside Google

* Roll engine to e976be13c51448f89107d082ec81e2b6731671fa

* move away from deprecated constants

Fixes some tests that weren't aggressively catching exceptions.
Fixes some actual failures that were found because of this.
Tries to fix an intermittent failure with crash1_test.dart which could be a race condition.

Also, make sure that broken tests actually break the bots.

And add a test to make sure that keeps happening.