[CP] ContentType with utf-8 not encoded properly in Dart 3.6 #59813
Description
Commit(s) to merge
https://dart-review.googlesource.com/c/sdk/+/402281
Target
stable
Prepared changelist for beta/stable
https://dart-review.googlesource.com/c/sdk/+/402422
Issue Description
HttpResponse.writeln does not honor the charset set by the developer. This is a regression from Dart 3.5.
What is the fix
Change the IOSink writeln method to delegate to its subclass' write method.
Why cherry-pick
The issue was found by a user. Any user using HttpServer with an explicit "Content-Type" and sending non-ISO-8859-1 (Latin-1) data might be affected.
Risk
Low.
The code change is a single line (that reverts a change made in another PR). The change includes 230 lines of tests that also pass in Dart 3.5 (but not in Dart 3.6).
Issue link(s)
Extra Info
No response