Use failedAt in more places

pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart

Index: pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
diff --git a/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
index 1754c5438bd2c69bc0a559c6a7b6a56ec72251ef..c953bd108bf275315db1097cb20b75686b869733 100644
--- a/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
@@ -220,12 +220,10 @@ class ParameterStubGenerator {
     if (member.enclosingClass != null && member.enclosingClass.isClosure) {
       ClosureClassElement cls = member.enclosingClass;
       if (cls.supertype.element == _commonElements.boundClosureClass) {
-        throw new SpannableAssertionFailure(
-            cls.methodElement, 'Bound closure1.');
+        failedAt(cls.methodElement, 'Bound closure1.');
       }
       if (cls.methodElement.isInstanceMember) {
-        throw new SpannableAssertionFailure(
-            cls.methodElement, 'Bound closure2.');
+        failedAt(cls.methodElement, 'Bound closure2.');
       }
     }