Support synthetic default constructors.

pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart

 // Copyright (c) 2013, 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 dart2js.ir_builder;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' show PrimitiveConstantValue;
 import '../dart_types.dart';
 import '../dart2jslib.dart';
 import '../elements/elements.dart';
 import '../source_file.dart';
 import '../tree/tree.dart' as ast;
 import '../scanner/scannerlib.dart' show Token, isUserDefinableOperator;
 import '../universe/universe.dart' show SelectorKind;
 import 'cps_ir_nodes.dart' as ir;
+import '../elements/modelx.dart' show SynthesizedConstructorElementX;
 
 part 'cps_ir_builder_visitor.dart';
 
 /// A mapping from variable elements to their compile-time values.
 ///
 /// Map elements denoted by parameters and local variables to the
 /// [ir.Primitive] that is their value.  Parameters and locals are
 /// assigned indexes which can be used to refer to them.
 class Environment {
   /// A map from elements to their environment index.
@@ skipping 1526 matching lines @@
     index = 0;
     for (int i = 0; i < environment.length; ++i) {
       if (common[i] == null) {
         environment.index2value[i] = parameters[index++];
       }
     }
 
     return join;
   }
 }