[kernel] Report error for dangling node reference in metadata
[kernel] Report error for dangling node reference in metadata

Currently, kernel metadata does not support references to nodes which
are not reachable from root Component. This CL adds an error if such
reference exists, instead of silently writing zero offset.

Change-Id: I6de886296bea66bd732f379cc99e0e3693ea79af
Reviewed-on: https://dart-review.googlesource.com/52527
Commit-Queue: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>
Reviewed-by: Kevin Millikin <a6737c91ef81c790d8ad0ae8762bd5b2332a6e42@google.com>

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