Refactor and simplify the dart2dart renamer.

sdk/lib/_internal/compiler/implementation/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 'cps_ir_nodes.dart' as ir;
 import '../elements/elements.dart';
 import '../dart2jslib.dart';
 import '../dart_types.dart';
@@ skipping 92 matching lines @@
     // and generating the correct syntax.
     if (element.isGetter || element.isSetter) return false;
 
     // TODO(lry): support native functions (also in [visitReturn]).
     if (function.isNative) return false;
 
     // TODO(kmillikin,sigurdm): support syntax for redirecting factory
     if (function is ConstructorElement && function.isRedirectingFactory) {
       return false;
     }
+    // TODO(kmillikin,sigurdm): support syntax for factory constructors
+    if (function is ConstructorElement && function.isFactoryConstructor) {
+      return false;
+    }
 
     return true;
   }
 
   bool get inCheckedMode {
     bool result = false;
     assert((result = true));
     return result;
   }
 
@@ skipping 1686 matching lines @@
   }
 
   visitFunctionExpression(ast.FunctionExpression node) {
     FunctionElement oldFunction = currentFunction;
     currentFunction = elements[node];
     visit(node.body);
     currentFunction = oldFunction;
   }
 
 }