This will allow users who are implementing their own deferred loading mechanism
to batch all the loads for a specific library. Today in order to do batching users have to gather the URIs passed to the `dartDeferedLibraryLoader` hook in a list and schedule (e.g. via setTimeout) a load for some future task.
The need to schedule a task has been shown to cause delays in IPL. But loading each part file individually can also be very expensive. So this allows for a compromise where bundling can be done synchronously per loaded library.
Adds ~8kB to unminified main files and ~2.5kB to minified main files.
Bug: https://github.com/dart-lang/sdk/issues/54202
Change-Id: I623643b03920988cda8b0f8b297944be35ffa606
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340480
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>
Nate Biggs