Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/rasta/issue_000081.dart.outline.expect

Index: pkg/front_end/testcases/rasta/issue_000081.dart.outline.expect
diff --git a/pkg/front_end/testcases/rasta/issue_000081.dart.outline.expect b/pkg/front_end/testcases/rasta/issue_000081.dart.outline.expect
index 0ad6433fe07ce50f87824b9e4dfbfbccf3ba91a2..246e0c779dbeaeed4e7089eb4dcd629f04b5e544 100644
--- a/pkg/front_end/testcases/rasta/issue_000081.dart.outline.expect
+++ b/pkg/front_end/testcases/rasta/issue_000081.dart.outline.expect
@@ -4,12 +4,12 @@ import "dart:core" as core;
 
 class Base extends core::Object {
   field core::int hashCode;
-  constructor •() → void
+  default constructor •() → void
     ;
 }
 class Sub extends self::Base {
   field core::int _hashCode;
-  constructor •() → void
+  default constructor •() → void
     ;
   get hashCode() → dynamic
     ;