Use failedAt in more places

pkg/compiler/lib/src/js_backend/mirrors_data.dart

 // Copyright (c) 2017, 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.
 
 import '../closure.dart';
 import '../common.dart';
 import '../common_elements.dart';
 import '../compiler.dart';
 import '../constants/values.dart';
 import '../elements/elements.dart';
@@ skipping 537 matching lines @@
     for (LocalFunctionElement closure in worldBuilder.localFunctions) {
       closureMap.putIfAbsent(closure.enclosingClass, () => []).add(closure);
     }
     bool foundClosure = false;
     for (ClassElement cls in worldBuilder.directlyInstantiatedClasses) {
       // Do not process internal classes.
       if (cls.library.isInternalLibrary || cls.isInjected) continue;
       if (isClassReferencedFromMirrorSystem(cls)) {
         Set<Name> memberNames = new Set<Name>();
         // 1) the class (should be resolved)
-        assert(invariant(cls, cls.isResolved));
+        assert(cls.isResolved, failedAt(cls));
         _classesNeededForReflection.add(cls);
         // 2) its constructors (if resolved)
         cls.constructors.forEach((ConstructorElement constructor) {
           if (worldBuilder.isMemberUsed(constructor)) {
             _membersNeededForReflection.add(constructor);
           }
         });
         // 3) all members, including fields via getter/setters (if resolved)
         cls.forEachClassMember((Member member) {
           MemberElement element = member.element;
           if (worldBuilder.isMemberUsed(element)) {
             memberNames.add(member.name);
             _membersNeededForReflection.add(element);
             element.nestedClosures
                 .forEach((SynthesizedCallMethodElementX callFunction) {
               _membersNeededForReflection.add(callFunction);
               _classesNeededForReflection.add(callFunction.closureClass);
             });
           }
         });
         // 4) all overriding members of subclasses/subtypes (should be resolved)
         if (closedWorld.hasAnyStrictSubtype(cls)) {
           closedWorld.forEachStrictSubtypeOf(cls, (ClassElement subcls) {
             subcls.forEachClassMember((Member member) {
               if (memberNames.contains(member.name)) {
                 // TODO(20993): find out why this assertion fails.
-                // assert(invariant(member.element,
-                //    worldBuilder.isMemberUsed(member.element)));
+                // assert(worldBuilder.isMemberUsed(member.element),
+                //     failedAt(member.element));
                 if (worldBuilder.isMemberUsed(member.element)) {
                   _membersNeededForReflection.add(member.element);
                 }
               }
             });
           });
         }
         // 5) all its closures
         List<LocalFunctionElement> closures = closureMap[cls];
         if (closures != null) {
@@ skipping 93 matching lines @@
   }
 
   /// Called when `const Symbol(name)` is seen.
   void registerConstSymbol(String name) {
     symbolsUsed.add(name);
     if (name.endsWith('=')) {
       symbolsUsed.add(name.substring(0, name.length - 1));
     }
   }
 }