anchor.diff:                checkAstDerivedDataOverride: true,
                 prefixExpectations: [
                   new _PrefixExpectation(ReferenceKind.unresolved, 'C'),
  -                new _PrefixExpectation(ReferenceKind.prefix, 'p',
  -                    inLibraryDefiningUnit: true)
  +                new _PrefixExpectation(ReferenceKind.prefix, 'p')
                 ])
       ]);
     }
  
positive.code:     } else if (prefixExpectations != null) {
        for (_PrefixExpectation expectation in prefixExpectations) {
          expect(reference.prefixReference, isNot(0));
          reference = checkReferenceIndex(
              reference.prefixReference,
              expectation.inLibraryDefiningUnit
                  ? null
                  : expectation.absoluteUri ?? absoluteUri,
              expectation.inLibraryDefiningUnit
                  ? null
                  : expectation.relativeUri ?? relativeUri,
              expectation.name,
              expectedKind: expectation.kind,
              checkAstDerivedDataOverride: checkAstDerivedDataOverride,
              expectedTargetUnit: expectedTargetUnit,
  
negative.code:               prefixExpectations: [
                  new _PrefixExpectation(ReferenceKind.classOrEnum, 'C',
                      absoluteUri: absUri('/a.dart'), relativeUri: 'a.dart'),
                  new _PrefixExpectation(ReferenceKind.prefix, 'p')
                ])
      ]);
    }
  