Set 'isSyntheticDefault' for default constructors.

pkg/front_end/testcases/covariant_generic.dart.strong.expect

Index: pkg/front_end/testcases/covariant_generic.dart.strong.expect
diff --git a/pkg/front_end/testcases/covariant_generic.dart.strong.expect b/pkg/front_end/testcases/covariant_generic.dart.strong.expect
index 1e99fae14bc5db0d02d9df0648da36f9348d5c67..cf4a1f65f6934467af519581892c404445907d9d 100644
--- a/pkg/front_end/testcases/covariant_generic.dart.strong.expect
+++ b/pkg/front_end/testcases/covariant_generic.dart.strong.expect
@@ -15,12 +15,6 @@ class Foo<T extends core::Object> extends core::Object {
   method withCallback((self::Foo::T) → void callback) → void {
     callback.call(this.{self::Foo::finalField});
   }
-  set mutableField$cc(core::Object mutableField_) → dynamic

[ahe, 2017/07/14 09:42:26]

I'm not sure this is correct. I think these are covariant bridge methods that
are needed to perform additional runtime checks. This is what Asger was working
on, and my understanding is that we planned to use that work.

-    this.{=self::Foo::mutableField} = mutableField_ as self::Foo::T;
-  method method$cc(core::Object x) → void
-    this.{=self::Foo::method}(x as self::Foo::T);
-  set setter$cc(core::Object x) → void
-    this.{=self::Foo::setter} = x as self::Foo::T;
 }
 static method main() → dynamic {
   self::Foo<core::int> fooInt = new self::Foo::•<core::int>(1, (core::int x) → core::Null {});