Use failedAt in more places (js_emitter)

pkg/compiler/lib/src/js_emitter/program_builder/collector.dart

 // Copyright (c) 2015, 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.
 
 part of dart2js.js_emitter.program_builder;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 262 matching lines @@
     }
 
     // 4. Finally, sort the classes.
     List<ClassEntity> sortedClasses = _sorter.sortClasses(neededClasses);
 
     for (ClassEntity cls in sortedClasses) {
       if (_nativeData.isNativeOrExtendsNative(cls) &&
           !classesOnlyNeededForRti.contains(cls)) {
         // For now, native classes and related classes cannot be deferred.
         nativeClassesAndSubclasses.add(cls);
-        assert(invariant(cls, !_deferredLoadTask.isDeferredClass(cls)));
+        assert(!_deferredLoadTask.isDeferredClass(cls), failedAt(cls));
         outputClassLists
             .putIfAbsent(_deferredLoadTask.mainOutputUnit,
                 () => new List<ClassElement>())
             .add(cls);
       } else {
         outputClassLists
             .putIfAbsent(_deferredLoadTask.outputUnitForClass(cls),
                 () => new List<ClassElement>())
             .add(cls);
       }
@@ skipping 61 matching lines @@
   }
 
   void collect() {
     computeNeededDeclarations();
     computeNeededConstants();
     computeNeededStatics();
     computeNeededStaticNonFinalFields();
     computeNeededLibraries();
   }
 }