This should reduce the number of flakes without actually increasing
the timeout, so we'll still find out quickly if a test is hanging.
The numbers here might need tweaking. Maybe the default two seconds is
too short for CI bots.
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.
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.
