Use failedAt in more places

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

 // Copyright (c) 2011, 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 js_backend.namer;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class MinifyNamer extends Namer
@@ skipping 334 matching lines @@
             cls, new _ConstructorBodyNamingScope(cls.superclass, registry));
       } else {
         return new _ConstructorBodyNamingScope.forClass(
             cls, new _ConstructorBodyNamingScope(cls.superclass, registry));
       }
     });
   }
 
   String constructorBodyKeyFor(ConstructorBodyElement body) {
     int position = _constructors.indexOf(body.constructor);
-    assert(invariant(body, position >= 0, message: "constructor body missing"));
+    assert(position >= 0, failedAt(body, "constructor body missing"));
     return "@constructorBody@${_startIndex + position}";
   }
 }
 
 abstract class _MinifyConstructorBodyNamer implements Namer {
   Map<ClassElement, _ConstructorBodyNamingScope> _constructorBodyScopes =
       new Map<ClassElement, _ConstructorBodyNamingScope>();
 
   @override
   jsAst.Name constructorBodyName(FunctionElement method) {
@@ skipping 17 matching lines @@
     String prefix =
         selector.isGetter ? r"$get" : selector.isSetter ? r"$set" : "";
     String callSuffix = selector.isCall
         ? callSuffixForStructure(selector.callStructure).join()
         : "";
     String suffix = suffixForGetInterceptor(classes);
     String fullName = "\$intercepted$prefix\$$root$callSuffix\$$suffix";
     return _disambiguateInternalGlobal(fullName);
   }
 }