[vm] Skip functions in source reports if their token pos is unknown
[vm] Skip functions in source reports if their token pos is unknown

Change-Id: I2f953ee5745dd7193a77098d0e83d5ac247f5886
Reviewed-on: https://dart-review.googlesource.com/43720
Commit-Queue: Dmitry Stefantsov <95a4b7e39916a54bd6477bec6a6de014b977db32@google.com>
Reviewed-by: Jens Johansen <05223a3c6bdf76af6f84755eae231abeebcf4530@google.com>
Reviewed-by: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>

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