[kernel] Print errors in a nicer format.
[kernel] Print errors in a nicer format.

BUG=
R=kmillikin@google.com

Review URL: https://chromereviews.googleplex.com/508597013 .

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