Force lf-lineendings for .dart-files.
Force lf-lineendings for .dart-files.

This ensures that Windows-produced kernel files have source offset that match kernel files produced on other platforms.

Bug: https://github.com/flutter/flutter/issues/22497
Change-Id: I6c1e044a423ea069cd523a6469804efbc0c0b2e2
Reviewed-on: https://dart-review.googlesource.com/77667
Reviewed-by: Zach Anderson <9f8b31e960a68dade71618f1ff6da6e23a1edfc9@google.com>
Commit-Queue: Alexander Aprelev <dfb74c35a357c2059971a4bf7fe26b6a7c18085d@google.com>

dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk