dart2js should generate absolute "file:" URIs in sourcemaps for internal libraries

[nex3]

When dart2js generates sourcemaps with references to the internal libraries, it produces relative URLs. This breaks on "pub serve", since the internal Dart libraries aren't being served. It should instead generate absolute "file:" URLs.

[nex3]

Marked this as blocking #17460.

[johnniwinther]

For which libraries do you need absolute paths?

All libraries?
API internal libraries, i.e. dart:_* libraries?
API libraries, i.e. dart:* libraries?
Package libraries?

Why can't these be served as well?

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Set owner to @johnniwinther.
Added NeedsInfo label.

[DartBot]

This comment was originally written by @zoechi

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As far as my experience with source maps goes
file URIs are only allowed when the entry page was opened using a file URI.
Opening the file from pub serve and loading some additional files from file URI doesn't work.

[nex3]

We could potentially serve the Dart SDK libraries. Currently it's difficult to communicate to dart2js where the SDK is on the server, though, since it takes and emits paths only in terms of the filesystem.

[sigmundch]

combining with #20259