Use failedAt in more places (misc2)

pkg/compiler/lib/src/elements/elements.dart

 // Copyright (c) 2012, 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.
 
 library elements;
 
 import 'package:front_end/src/fasta/parser/async_modifier.dart'
     show AsyncModifier;
 
 import '../common.dart';
@@ skipping 808 matching lines @@
    * Precondition: `callStructure.signatureApplies(element.type)`.
    *
    * Invariant: [element] must be the implementation element.
    */
   static List<T> makeArgumentsList<T>(
       CallStructure callStructure,
       Link<Node> arguments,
       FunctionElement element,
       T compileArgument(Node argument),
       T compileDefaultValue(ParameterElement element)) {
-    assert(invariant(element, element.isImplementation));
+    assert(element.isImplementation, failedAt(element));
     List<T> result = <T>[];
 
     FunctionSignature parameters = element.functionSignature;
     parameters.forEachRequiredParameter((ParameterElement element) {
       result.add(compileArgument(arguments.head));
       arguments = arguments.tail;
     });
 
     if (!parameters.optionalParametersAreNamed) {
       parameters.forEachOptionalParameter((ParameterElement element) {
@@ skipping 1192 matching lines @@
   /// by a field.
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }