anchor.diff:  ///
   /// Clients may not extend, implement or mix-in this class.
   abstract class AugmentedClassOrEnumElement
  -    implements AugmentedInterfaceDefiningElement {
  +    implements AugmentedInterfaceElement {
     /// Returns constructors declared in this element.
     ///
     /// [ConstructorAugmentationElement]s replace corresponding elements,
  
positive.code: abstract class MixinElement
      implements
          MixinOrAugmentationElement,
          InterfaceDefiningElement,
          _TmpSharedClassElement {
    /// Returns the result of applying augmentations to this element.
    AugmentedMixinElement get augmented;
  
negative.code: /// Clients may not extend, implement or mix-in this class.
  @experimental
  abstract class MixinOrAugmentationElement
      implements InterfaceOrAugmentationElement {
    /// The immediate augmentation of this element, or `null` if there are no
    /// augmentations. [MixinAugmentationElement.augmentationTarget] is the back
    /// pointer that will point at this element.
  