Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/rasta/class_hierarchy.dart.direct.expect

Index: pkg/front_end/testcases/rasta/class_hierarchy.dart.direct.expect
diff --git a/pkg/front_end/testcases/rasta/class_hierarchy.dart.direct.expect b/pkg/front_end/testcases/rasta/class_hierarchy.dart.direct.expect
index f8bf7421b7db0c1dfe112c67293f5ae3b65b4e25..e60c91b3145fc0aa8f75ba3d5529e901b061130c 100644
--- a/pkg/front_end/testcases/rasta/class_hierarchy.dart.direct.expect
+++ b/pkg/front_end/testcases/rasta/class_hierarchy.dart.direct.expect
@@ -3,11 +3,11 @@ import self as self;
 import "dart:core" as core;
 
 class A extends core::Object {
-  constructor •() → self::A
+  default constructor •() → self::A
     : invalid-initializer;
 }
 class B extends core::Object {
-  constructor •() → self::B
+  default constructor •() → self::B
     : invalid-initializer;
 }
 class C extends core::Object {