Fixed missing method referenced when MallocHooks is unsupported.

runtime/observatory/lib/src/elements/code_ref.dart

Index: runtime/observatory/lib/src/elements/code_ref.dart
diff --git a/runtime/observatory/lib/src/elements/code_ref.dart b/runtime/observatory/lib/src/elements/code_ref.dart
index 14b783bd92c47eb3d555f78b3c0817ab2a8184ee..f262cf442e48ec59778aeecebd1053168df8a28d 100644
--- a/runtime/observatory/lib/src/elements/code_ref.dart
+++ b/runtime/observatory/lib/src/elements/code_ref.dart
@@ -27,7 +27,6 @@ class CodeRefElement extends HtmlElement implements Renderable {
 
   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);
@@ -55,7 +54,7 @@ class CodeRefElement extends HtmlElement implements Renderable {
     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
     ];