anchor.diff:    /// A list containing all of the variables contained in this compilation unit.
     List<TopLevelVariableElement> _variables;
   
  -  /// Resynthesized explicit top-level property accessors.
  -  UnitExplicitTopLevelAccessors _explicitTopLevelAccessors;
  -
  -  /// Resynthesized explicit top-level variables.
  -  UnitExplicitTopLevelVariables _explicitTopLevelVariables;
  -
     /// Initialize a newly created compilation unit element to have the given
     /// [name].
     CompilationUnitElementImpl()
  
positive.code:   }
  }
  
  /// Container with information about explicit top-level property accessors and
  /// corresponding implicit top-level variables.
  class UnitExplicitTopLevelAccessors {
    final List<PropertyAccessorElementImpl> accessors =
        <PropertyAccessorElementImpl>[];
    final List<TopLevelVariableElementImpl> implicitVariables =
        <TopLevelVariableElementImpl>[];
  }
  
  /// Container with information about explicit top-level variables and
  /// corresponding implicit top-level property accessors.
  class UnitExplicitTopLevelVariables {
    final List<TopLevelVariableElementImpl> variables;
    final List<PropertyAccessorElementImpl> implicitAccessors =
        <PropertyAccessorElementImpl>[];
  
    UnitExplicitTopLevelVariables(int numberOfVariables)
        : variables = numberOfVariables != 0
              ? new List<TopLevelVariableElementImpl>(numberOfVariables)
              : const <TopLevelVariableElementImpl>[];
  }
  
  /// A concrete implementation of a [UriReferencedElement].
  abstract class UriReferencedElementImpl extends ElementImpl
      implements UriReferencedElement {
  
negative.code:       _createPropertiesAndAccessors(this);
        assert(_accessors != null);
        return _accessors;
      }
  
      return _accessors ?? const <PropertyAccessorElement>[];
  