This relands commit ff34fd8110,
but puts tree shaking of write-only fields under the flag which is
disabled by default.
So far tree shaking was removing fields which are not used at all.
This change improves tree shaking of fields so fields
which are only written or used as interface targets can be removed.
The following limitations apply:
* Field is not removed if there is a constant object with that field, as
it may impact identity of constant objects which is an observable
behavior.
* Instance field is not removed if it has a non-trivial initializer as
it may have side-effects when executed by constructors.
* Late final fields are not removed, as writing such fields may have
side-effect.
* When field is removed, we may need to introduce an abstract getter
or abstract setter if field is used as a target of an interface call.
If a field was written, then setter would be non-abstract (but empty).
Issue https://github.com/dart-lang/sdk/issues/35310
Change-Id: Iec75b8301892664f4f955a01e5960b17e6620531
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143286
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Alexander Aprelev