Fixed missing method referenced when MallocHooks is unsupported.

runtime/observatory/lib/src/elements/function_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 function_ref_element;
 
 import 'dart:html';
 import 'dart:async';
 import 'package:observatory/models.dart' as M
     show
@@ skipping 18 matching lines @@
   M.IsolateRef _isolate;
   M.FunctionRef _function;
   bool _qualified;
 
   M.IsolateRef get isolate => _isolate;
   M.FunctionRef get function => _function;
   bool get qualified => _qualified;
 
   factory FunctionRefElement(M.IsolateRef isolate, M.FunctionRef function,
       {bool qualified: true, RenderingQueue queue}) {
-    assert(isolate != null);
     assert(function != null);
     assert(qualified != null);
     FunctionRefElement e = document.createElement(tag.name);
     e._r = new RenderingScheduler(e, queue: queue);
     e._isolate = isolate;
     e._function = function;
     e._qualified = qualified;
     return e;
   }
 
   FunctionRefElement.created() : super.created();
 
   @override
   void attached() {
     super.attached();
     _r.enable();
   }
 
   @override
   void detached() {
     super.detached();
     children = [];
     title = '';
     _r.disable(notify: true);
   }
 
   void render() {
     var content = <Element>[
       new AnchorElement(
-          href: M.isSyntheticFunction(_function.kind)
+          href: (M.isSyntheticFunction(_function.kind) || (_isolate == null))
               ? null
               : Uris.inspect(_isolate, object: _function))
         ..text = _function.name
     ];
     if (qualified) {
       M.ObjectRef owner = _function.dartOwner;
       while (owner is M.FunctionRef) {
         M.FunctionRef function = (owner as M.FunctionRef);
         content.addAll([
           new SpanElement()..text = '.',
           new AnchorElement(
-              href: M.isSyntheticFunction(function.kind)
+              href: (M.isSyntheticFunction(function.kind) || (_isolate == null))
                   ? null
                   : Uris.inspect(_isolate, object: function))
             ..text = function.name
         ]);
         owner = function.dartOwner;
       }
       if (owner is M.ClassRef) {
         content.addAll([
           new SpanElement()..text = '.',
           new ClassRefElement(_isolate, owner, queue: _r.queue)
         ]);
       }
     }
     children = content.reversed.toList(growable: false);
     title = M.getFunctionFullName(_function);
   }
 }