Add flag to track if a constructor is the synthetic default constructor.

pkg/kernel/lib/text/ast_to_text.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library kernel.ast_to_text;
 
 import '../ast.dart';
 import '../import_table.dart';
 
 class Namer<T> {
   int index = 0;
@@ skipping 715 matching lines @@
       writeWord("/* from ${node.fileUri} */");
     }
     writeFunction(node.function, name: getMemberName(node));
   }
 
   visitConstructor(Constructor node) {
     writeAnnotationList(node.annotations);
     writeIndentation();
     writeModifier(node.isExternal, 'external');
     writeModifier(node.isConst, 'const');
+    writeModifier(node.isSyntheticDefault, 'default');
     writeWord('constructor');
     writeFunction(node.function,
         name: node.name, initializers: node.initializers);
   }
 
   visitClass(Class node) {
     writeAnnotationList(node.annotations);
     writeIndentation();
     writeModifier(node.isAbstract, 'abstract');
     writeWord('class');
@@ skipping 897 matching lines @@
   }
   throw 'illegal ProcedureKind: $kind';
 }
 
 class ExpressionPrinter {
   final Printer writeer;
   final int minimumPrecedence;
 
   ExpressionPrinter(this.writeer, this.minimumPrecedence);
 }