Missed adding the isExternal property to all VM MethodMirror subclasses.

runtime/lib/mirrors_impl.dart

 // Copyright (c) 2012, 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.
 
 // VM-specific implementation of the dart:mirrors library.
 
 import "dart:collection" show UnmodifiableListView, UnmodifiableMapView;
 import "dart:async" show Future;
 
 var dirty = false;
@@ skipping 275 matching lines @@
                      this.isTopLevel,
                      this._target);
 
   bool get isSynthetic => true;
   bool get isRegularMethod => false;
   bool get isOperator => false;
   bool get isConstructor => false;
   bool get isConstConstructor => false;
   bool get isGenerativeConstructor => false;
   bool get isFactoryConstructor => false;
+  bool get isExternal => false;
   bool get isRedirectingConstructor => false;
   bool get isAbstract => false;
 
   bool get isSetter => !isGetter;
   bool get isPrivate => _n(simpleName).startsWith('_');
 
   Symbol get qualifiedName => _computeQualifiedName(owner, simpleName);
   Symbol get constructorName => const Symbol('');
 
   TypeMirror get returnType => _target.type;
@@ skipping 1360 matching lines @@
     if (typeMirror == null) {
       typeMirror = makeLocalTypeMirror(key);
       _instanitationCache[key] = typeMirror;
       if (typeMirror is ClassMirror && !typeMirror._isGeneric) {
         _declarationCache[key] = typeMirror;
       }
     }
     return typeMirror;
   }
 }