Improve error reporting when a mixin application is invalid.

pkg/analyzer/lib/src/generated/element_handle.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.element_handle;
 
 import 'ast.dart';
@@ skipping 97 matching lines @@
   bool isSuperConstructorAccessible(ConstructorElement constructor) =>
       actualElement.isSuperConstructorAccessible(constructor);
 
   @override
   bool get isTypedef => actualElement.isTypedef;
 
   @override
   bool get isValidMixin => actualElement.isValidMixin;
 
   @override
+  bool get mixinErrorsReported => actualElement.mixinErrorsReported;
+
+  @override
   MethodElement lookUpConcreteMethod(String methodName, LibraryElement library) => actualElement.lookUpConcreteMethod(methodName, library);
 
   @override
   PropertyAccessorElement lookUpGetter(String getterName, LibraryElement library) => actualElement.lookUpGetter(getterName, library);
 
   @override
   PropertyAccessorElement lookUpInheritedConcreteGetter(String methodName, LibraryElement library) => actualElement.lookUpInheritedConcreteGetter(methodName, library);
 
   @override
   MethodElement lookUpInheritedConcreteMethod(String methodName, LibraryElement library) => actualElement.lookUpInheritedConcreteMethod(methodName, library);
@@ skipping 877 matching lines @@
   VariableElement get actualElement => super.actualElement as VariableElement;
 }
 /**
  * TODO(scheglov) invalid implementation
  */
 class WeakReference<T> {
   final T value;
   WeakReference(this.value);
   T get() => value;
 }