There's very little code-sharing between the two, and what little there
is is concentrated in the GenSnapshotClass and the fingerprint
reading/writing utility methods.
Wraps the compile function in a class injected via the global context,
which makes it easier to mock in unit tests -- specifically tests for
AOT snapshotting, which already require pretty significant amounts of
mock inputs.
* Handle error count reported by frontend.
Extend compilation result from single string to a structure(string filename and integer error count).
* Use ?.
* Include engine roll with dart sdk roll.
* parse(onError) -> tryParse
* Make '?? throw' more readable and avoid issue with analyzer
* Fix test so it mocks compiler output including errors count
