Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/unused_methods.dart.outline.expect

Index: pkg/front_end/testcases/unused_methods.dart.outline.expect
diff --git a/pkg/front_end/testcases/unused_methods.dart.outline.expect b/pkg/front_end/testcases/unused_methods.dart.outline.expect
index 860b54f6e52683719b27b481a417348b60570269..3065d87ae73cc5f1205aa697468ba33d5e6825b5 100644
--- a/pkg/front_end/testcases/unused_methods.dart.outline.expect
+++ b/pkg/front_end/testcases/unused_methods.dart.outline.expect
@@ -7,7 +7,7 @@ class UnusedClass extends core::Object {
     ;
 }
 abstract class UsedAsBaseClass extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     ;
   method usedInSubclass() → void
     ;
@@ -17,25 +17,25 @@ abstract class UsedAsBaseClass extends core::Object {
     ;
 }
 class UsedAsInterface extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     ;
   method usedInSubclass() → void
     ;
 }
 class InstantiatedButMethodsUnused extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     ;
   method usedInSubclass() → void
     ;
 }
 class ClassA extends self::UsedAsBaseClass implements self::UsedAsInterface, self::InstantiatedButMethodsUnused {
-  constructor •() → void
+  default constructor •() → void
     ;
   method usedInSubclass() → void
     ;
 }
 class ClassB extends self::UsedAsBaseClass implements self::UsedAsInterface, self::InstantiatedButMethodsUnused {
-  constructor •() → void
+  default constructor •() → void
     ;
   method usedInSubclass() → void
     ;