Add type inference logic for map literals

pkg/front_end/testcases/inference/inferred_type_is_typedef.dart

Index: pkg/front_end/testcases/inference/inferred_type_is_typedef.dart
diff --git a/pkg/front_end/testcases/inference/inferred_type_is_typedef.dart b/pkg/front_end/testcases/inference/inferred_type_is_typedef.dart
index 3e2e8ad9a9d060b073ee8ab9397e463b086cead1..fa8c890c44969dfd15497deeacef2979b47520b5 100644
--- a/pkg/front_end/testcases/inference/inferred_type_is_typedef.dart
+++ b/pkg/front_end/testcases/inference/inferred_type_is_typedef.dart
@@ -7,3 +7,7 @@ library test;
 
 typedef void F();
 final /*@topType=Map<String, () -> void>*/ x = <String, F>{};
+
+main() {
+  x;
+}