Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/inference/infer_assign_to_index_set_vs_get.dart.outline.expect

Index: pkg/front_end/testcases/inference/infer_assign_to_index_set_vs_get.dart.outline.expect
diff --git a/pkg/front_end/testcases/inference/infer_assign_to_index_set_vs_get.dart.outline.expect b/pkg/front_end/testcases/inference/infer_assign_to_index_set_vs_get.dart.outline.expect
index 6c8e6de9139f9cf75f2a76277ae412f3ec31b1ff..62690b3e4fd7c76ee25260d2f3ffdc7eb7b59220 100644
--- a/pkg/front_end/testcases/inference/infer_assign_to_index_set_vs_get.dart.outline.expect
+++ b/pkg/front_end/testcases/inference/infer_assign_to_index_set_vs_get.dart.outline.expect
@@ -3,11 +3,11 @@ import self as self;
 import "dart:core" as core;
 
 class Index extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     ;
 }
 class A extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     ;
   operator +(self::F v) → self::C
     ;
@@ -15,7 +15,7 @@ class A extends core::Object {
     ;
 }
 class B extends self::A {
-  constructor •() → void
+  default constructor •() → void
     ;
   operator +(self::E v) → self::D
     ;
@@ -23,23 +23,23 @@ class B extends self::A {
     ;
 }
 class C extends self::B {
-  constructor •() → void
+  default constructor •() → void
     ;
 }
 class D extends self::C {
-  constructor •() → void
+  default constructor •() → void
     ;
 }
 class E extends self::D {
-  constructor •() → void
+  default constructor •() → void
     ;
 }
 class F extends self::E {
-  constructor •() → void
+  default constructor •() → void
     ;
 }
 class Test extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     ;
   operator [](self::Index i) → self::B
     ;