anchor.diff:  
     void resolve() {
       for (var unit in _libraryElement.units) {
  +      _unitElement = unit;
         for (var classElement in unit.types) {
           _classElement = classElement;
           for (var constructorElement in classElement.constructors) {
  
positive.code:       return;
      }
  
      for (var initializer in initializers) {
        _astResolver.resolve(
          initializer,
  
negative.code:   final Linker _linker;
    final LibraryElementImpl _libraryElement;
  
    CompilationUnitElement _unitElement;
    ClassElement _classElement;
    ConstructorElement _constructorElement;
    ConstructorDeclarationImpl _constructorNode;
  