Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/inference/infer_assign_to_index_super_upwards.dart.strong.expect

Index: pkg/front_end/testcases/inference/infer_assign_to_index_super_upwards.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/infer_assign_to_index_super_upwards.dart.strong.expect b/pkg/front_end/testcases/inference/infer_assign_to_index_super_upwards.dart.strong.expect
index d6c2a82d0c3eeea42cd6eaf6e66a8d35be40fe70..24e6d76d929552e91acbbb504a8e54918460f241 100644
--- a/pkg/front_end/testcases/inference/infer_assign_to_index_super_upwards.dart.strong.expect
+++ b/pkg/front_end/testcases/inference/infer_assign_to_index_super_upwards.dart.strong.expect
@@ -3,7 +3,7 @@ import self as self;
 import "dart:core" as core;
 
 abstract class Base<T extends core::Object, U extends core::Object> extends core::Object {
-  constructor •() → void
+  default constructor •() → void
     : super core::Object::•()
     ;
   operator [](core::String s) → self::Base::T
@@ -14,7 +14,7 @@ abstract class Base<T extends core::Object, U extends core::Object> extends core
   abstract method setValue(core::String s, self::Base::U v) → void;
 }
 abstract class Test1 extends self::Base<core::int, core::int> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -29,7 +29,7 @@ abstract class Test1 extends self::Base<core::int, core::int> {
   }
 }
 abstract class Test2 extends self::Base<core::int, core::num> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -47,7 +47,7 @@ abstract class Test2 extends self::Base<core::int, core::num> {
   }
 }
 abstract class Test3 extends self::Base<core::int, core::double> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -63,7 +63,7 @@ abstract class Test3 extends self::Base<core::int, core::double> {
   }
 }
 abstract class Test4 extends self::Base<core::num, core::int> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -78,7 +78,7 @@ abstract class Test4 extends self::Base<core::num, core::int> {
   }
 }
 abstract class Test5 extends self::Base<core::num, core::num> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -96,7 +96,7 @@ abstract class Test5 extends self::Base<core::num, core::num> {
   }
 }
 abstract class Test6 extends self::Base<core::num, core::double> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -112,7 +112,7 @@ abstract class Test6 extends self::Base<core::num, core::double> {
   }
 }
 abstract class Test7 extends self::Base<core::double, core::int> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -127,7 +127,7 @@ abstract class Test7 extends self::Base<core::double, core::int> {
   }
 }
 abstract class Test8 extends self::Base<core::double, core::num> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {
@@ -145,7 +145,7 @@ abstract class Test8 extends self::Base<core::double, core::num> {
   }
 }
 abstract class Test9 extends self::Base<core::double, core::double> {
-  constructor •() → void
+  default constructor •() → void
     : super self::Base::•()
     ;
   method test() → void {