Fixed missing method referenced when MallocHooks is unsupported.

runtime/observatory/lib/src/elements/code_ref.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 code_ref_element;
 
 import 'dart:html';
 import 'dart:async';
 import 'package:observatory/models.dart' as M
     show IsolateRef, CodeRef, isSyntheticCode;
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/tag.dart';
 import 'package:observatory/src/elements/helpers/uris.dart';
 
 class CodeRefElement extends HtmlElement implements Renderable {
   static const tag = const Tag<CodeRefElement>('code-ref');
 
   RenderingScheduler<CodeRefElement> _r;
 
   Stream<RenderedEvent<CodeRefElement>> get onRendered => _r.onRendered;
 
   M.IsolateRef _isolate;
   M.CodeRef _code;
 
   M.IsolateRef get isolate => _isolate;
   M.CodeRef get code => _code;
 
   factory CodeRefElement(M.IsolateRef isolate, M.CodeRef code,
       {RenderingQueue queue}) {
-    assert(isolate != null);
     assert(code != null);
     CodeRefElement e = document.createElement(tag.name);
     e._r = new RenderingScheduler(e, queue: queue);
     e._isolate = isolate;
     e._code = code;
     return e;
   }
 
   CodeRefElement.created() : super.created();
 
   @override
   void attached() {
     super.attached();
     _r.enable();
   }
 
   @override
   void detached() {
     super.detached();
     children = [];
     _r.disable(notify: true);
   }
 
   void render() {
     final name = (_code.isOptimized ? '*' : '') + _code.name;
     children = [
       new AnchorElement(
-          href: M.isSyntheticCode(_code.kind)
+          href: ((M.isSyntheticCode(_code.kind)) || (_isolate == null))
               ? null
               : Uris.inspect(_isolate, object: _code))..text = name
     ];
   }
 }