Improve parsing of function expressions.

pkg/front_end/testcases/regress/issue_29979.dart.strong.expect

Index: pkg/front_end/testcases/regress/issue_29979.dart.strong.expect
diff --git a/pkg/front_end/testcases/regress/issue_29979.dart.strong.expect b/pkg/front_end/testcases/regress/issue_29979.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..4087641188eba99692c8480d7c3cede395d91bb6
--- /dev/null
+++ b/pkg/front_end/testcases/regress/issue_29979.dart.strong.expect
@@ -0,0 +1,7 @@
+library;
+import self as self;
+
+const field dynamic #errors = const <dynamic>["pkg/front_end/testcases/regress/issue_29979.dart:6:4: Error: A function expression can't have a name.\n  (f() {})();\n   ^"]/* from null */;
+static method main() → dynamic {
+  (let final dynamic f = () → dynamic {} in f).call();
+}