Adds a Fingerprinter utility class that can be used to compute unique
fingerprints for a set of input paths and build options, compare to the
output of a previous run, and skip the build action if no inputs or
options have changed. The existing Fingerprint class still does all the
heavy lifting. Fingerprinter adds common operations such as
reading/writing/comparing fingerprints and parsing depfiles.
This migrates existing uses of Fingerprint over to Fingerprinter.
This also adds better fingerprinting to AOT snapshotting, which
previously failed to include several options in its fingerprint
(--preview-dart-2, --prefer-shared-library).
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
