Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/store_load.dart.direct.expect

Index: pkg/front_end/testcases/store_load.dart.direct.expect
diff --git a/pkg/front_end/testcases/store_load.dart.direct.expect b/pkg/front_end/testcases/store_load.dart.direct.expect
index 166ecccfa830fa12d4f57e9cea116e80c9f98d4c..c2d374273bac1de36651de52663f566a567949b6 100644
--- a/pkg/front_end/testcases/store_load.dart.direct.expect
+++ b/pkg/front_end/testcases/store_load.dart.direct.expect
@@ -4,23 +4,23 @@ import "dart:core" as core;
 
 class Foo extends core::Object {
   field dynamic _field = null;
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
 }
 class FooValue extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
 }
 class Bar extends core::Object {
   field dynamic _field = null;
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
 }
 class BarValue extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
 }