Avoid patching in dart2dart.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.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.
 
 // IrNodes are kept in a separate library to have precise control over their
 // dependencies on other parts of the system.
 library dart2js.ir_nodes;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' as values show ConstantValue;
@@ skipping 550 matching lines @@
       this.defaultParameterValues);
 
   FunctionDefinition.abstract(this.element,
                               this.parameters,
                               this.defaultParameterValues)
       : this.returnContinuation = null,
         this.localConstants = const <ConstDeclaration>[];
 
   accept(Visitor visitor) => visitor.visitFunctionDefinition(this);
 
-  /// Returns `true` if this function is abstract.
+  /// Returns `true` if this function is abstract or external.
   ///
   /// If `true`, [body] and [returnContinuation] are `null` and [localConstants]
   /// is empty.
   bool get isAbstract => body == null;
 }
 
 List<Reference<Primitive>> _referenceList(Iterable<Primitive> definitions) {
   return definitions.map((e) => new Reference<Primitive>(e)).toList();
 }
 
@@ skipping 363 matching lines @@
       release(node.parameters[i]);
     }
   }
 
   void visitIsTrue(IsTrue node) {
     visitReference(node.value);
   }
 
 }