anchor.diff:  
   import 'dart:async';
   
  +import 'package:path/path.dart' as p;
   import 'package:stack_trace/stack_trace.dart';
   import 'package:unittest/unittest.dart';
   
  
positive.code:     ]).toTrace();
  
      expect(trace.toString(), equals(
          'user/code.dart 10:11  Foo.bar\n'
          'dart:core 10:11       Bar.baz\n'
          'user/code.dart 10:11  Foo.bar\n'
          'dart:core 10:11       Bar.baz\n'));
    });
  
  
negative.code:     });
    });
  
    var userSlashCode = p.join('user', 'code.dart');
    group('Chain.terse', () {
      test('makes each trace terse', () {
        var chain = new Chain([
  