Avoid patching in dart2dart.

pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart

 // Copyright (c) 2014, 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 dart_tree_printer;
 
 import '../constants/values.dart' as values;
 import '../dart_types.dart' as types;
 import '../dart2jslib.dart' as dart2js;
 import '../elements/elements.dart' as elements;
@@ skipping 915 matching lines @@
           param.type == null ? null : makeType(param.type),
           makeEmptyModifiers(), // TODO: Parameter modifiers?
           singleton(definition));
     }
   }
 
   tree.Modifiers makeEmptyModifiers() {
     return new tree.Modifiers(blankList());
   }
 
-  tree.Modifiers makeModifiers({bool isStatic: false,
+  tree.Modifiers makeModifiers({bool isExternal: false,
+                                bool isStatic: false,
                                 bool isAbstract: false,
                                 bool isFactory: false,
                                 bool isConst: false,
                                 bool isFinal: false,
                                 bool isVar: false}) {
     List<tree.Node> nodes = [];
+    if (isExternal) {
+      nodes.add(makeIdentifier('external'));
+    }
     if (isStatic) {
       nodes.add(makeIdentifier('static'));
     }
     if (isAbstract) {
       nodes.add(makeIdentifier('abstract'));
     }
     if (isFactory) {
       nodes.add(makeIdentifier('factory'));
     }
     if (isConst) {
@@ skipping 11 matching lines @@
   tree.Modifiers makeVarModifiers({bool isConst: false,
                                    bool isFinal: false,
                                    bool useVar: false}) {
     return makeModifiers(isConst: isConst,
                          isFinal: isFinal,
                          isVar: useVar && !(isConst || isFinal));
   }
 
   tree.Modifiers makeFunctionModifiers(FunctionExpression exp) {
     if (exp.element == null) return makeEmptyModifiers();
-    return makeModifiers(isStatic: exp.element.isStatic,
+    return makeModifiers(isExternal: exp.element.isExternal,
+                         isStatic: exp.element.isStatic,
                          isFactory: exp.element.isFactoryConstructor);
   }
 
   tree.Node makeNodeForClassElement(elements.ClassElement cls) {
     if (cls.isMixinApplication) {
       return makeNamedMixinApplication(cls);
     } else {
       return makeClassNode(cls);
     }
   }
@@ skipping 223 matching lines @@
             printStringChunk(chunk.previous),
             node);
       } else {
         return node;
       }
     }
     return printStringChunk(output.chunk);
   }
 
 }