0310c8e233
This is a reland of 851d821556
Original change's description:
> [dart2js] Address some feedback on constraints API.
>
> * Changes default namer to use the always unique uri#prefix of a
> deferred import.
> * Changes builder api for combiner nodes to take sets.
>
> Change-Id: Iab23db94a166560682a8c2bd4a78ebfd3e734353
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/218880
> Reviewed-by: Sigmund Cherem <sigmund@google.com>
> Commit-Queue: Joshua Litt <joshualitt@google.com>
Change-Id: I6394166be1f3ddebe19cc71f70fa5f5b26e05231
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/219128
Commit-Queue: Joshua Litt <joshualitt@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>