Annotate optional parameter inferred types in front end test cases.

pkg/front_end/testcases/inference/downwards_inference_initializing_formal_default_formal.dart

Index: pkg/front_end/testcases/inference/downwards_inference_initializing_formal_default_formal.dart
diff --git a/pkg/front_end/testcases/inference/downwards_inference_initializing_formal_default_formal.dart b/pkg/front_end/testcases/inference/downwards_inference_initializing_formal_default_formal.dart
index c5e42b4247e74bebe524d97be7d83db212af6238..b82f0e70c421f73b9166365642b428f344a578f5 100644
--- a/pkg/front_end/testcases/inference/downwards_inference_initializing_formal_default_formal.dart
+++ b/pkg/front_end/testcases/inference/downwards_inference_initializing_formal_default_formal.dart
@@ -16,5 +16,5 @@ class Foo {
 void f([List<int> l = /*@typeArgs=int*/ const [1]]) {}
 // We do this inference in an early task but don't preserve the infos.
 Function2<List<int>, String> g = /*@returnType=String*/ (
-        [llll = /*@typeArgs=int*/ const [1]]) =>
+        [/*@type=List<int>*/ llll = /*@typeArgs=int*/ const [1]]) =>
     "hello";