Avoid patching in dart2dart.

pkg/compiler/lib/src/elements/modelx.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 elements.modelx;
 
 import 'elements.dart';
 import '../constants/expressions.dart';
 import '../helpers/helpers.dart';  // Included for debug helpers.
 import '../tree/tree.dart';
@@ skipping 100 matching lines @@
   Element get patch {
     throw new UnsupportedError('patch is not supported on $this');
   }
 
   Element get origin {
     throw new UnsupportedError('origin is not supported on $this');
   }
 
   bool get isSynthesized => false;
 
-  bool get isForwardingConstructor => false;
-
   bool get isMixinApplication => false;
 
   bool get isLocal => false;
 
   // TODO(johnniwinther): This breaks for libraries (for which enclosing
   // elements are null) and is invalid for top level variable declarations for
   // which the enclosing element is a VariableDeclarations and not a compilation
   // unit.
   bool get isTopLevel {
     return enclosingElement != null && enclosingElement.isCompilationUnit;
@@ skipping 166 matching lines @@
   get resolvedAst => unsupported();
   get type => unsupported();
   get cachedNode => unsupported();
   get functionSignature => unsupported();
   get patch => null;
   get origin => this;
   get immediateRedirectionTarget => unsupported();
   get nestedClosures => unsupported();
   get memberContext => unsupported();
   get executableContext => unsupported();
+  get isExternal => unsupported();
 
   bool get isRedirectingFactory => unsupported();
 
   computeSignature(compiler) => unsupported();
 
   bool get hasFunctionSignature => false;
 
   get effectiveTarget => this;
 
   computeEffectiveTargetType(InterfaceType newType) => unsupported();
@@ skipping 1231 matching lines @@
   BaseFunctionElementX(String name,
                        ElementKind kind,
                        Modifiers this.modifiers,
                        Element enclosing,
                        bool hasNoBody)
       : super(name, kind, enclosing),
         _hasNoBody = hasNoBody {
     assert(modifiers != null);
   }
 
+  bool get isExternal => modifiers.isExternal;
+
   bool get isInstanceMember {
     return isClassMember
            && !isConstructor
            && !isStatic;
   }
 
   bool get hasFunctionSignature => functionSignatureCache != null;
 
   FunctionSignature computeSignature(Compiler compiler) {
     if (functionSignatureCache != null) return functionSignatureCache;
@@ skipping 1247 matching lines @@
   AstElement get definingElement;
 
   bool get hasResolvedAst => definingElement.hasTreeElements;
 
   ResolvedAst get resolvedAst {
     return new ResolvedAst(declaration,
         definingElement.node, definingElement.treeElements);
   }
 
 }