Use failedAt in more places

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

Index: pkg/compiler/lib/src/js_backend/namer_names.dart
diff --git a/pkg/compiler/lib/src/js_backend/namer_names.dart b/pkg/compiler/lib/src/js_backend/namer_names.dart
index 7e8e76fb37dcae9be473f580027a288712d0cd86..d33c8694f588c116034648b1a9d813064444323a 100644
--- a/pkg/compiler/lib/src/js_backend/namer_names.dart
+++ b/pkg/compiler/lib/src/js_backend/namer_names.dart
@@ -191,8 +191,10 @@ class TokenName extends _NamerName implements jsAst.ReferenceCountedAstNode {
   int get hashCode => super.hashCode;
 
   finalize() {
-    assert(invariant(NO_LOCATION_SPANNABLE, !isFinalized,
-        message: "TokenName($key)=$_name has already been finalized."));
+    assert(
+        !isFinalized,
+        failedAt(NO_LOCATION_SPANNABLE,
+            "TokenName($key)=$_name has already been finalized."));
     _name = _scope.getNextName();
   }
 }