Add Function based profile tree

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

Index: runtime/observatory/lib/src/elements/observatory_element.dart
diff --git a/runtime/observatory/lib/src/elements/observatory_element.dart b/runtime/observatory/lib/src/elements/observatory_element.dart
index 9e9a363d7f0f0e4ac61ab68d212c94b27a37144a..cac26bcc687d65eb1ba21e593c965e848bb79479 100644
--- a/runtime/observatory/lib/src/elements/observatory_element.dart
+++ b/runtime/observatory/lib/src/elements/observatory_element.dart
@@ -97,8 +97,12 @@ class ObservatoryElement extends PolymerElement {
       if (obj is Isolate) {
         url = '${url}?isolateId=${Uri.encodeComponent(obj.id)}';
       } else {
+        if (obj.id == null) {
+          // No id
+          return url;
+        }
         url = ('${url}?isolateId=${Uri.encodeComponent(obj.isolate.id)}'
-               '&objectId=${Uri.encodeComponent(obj.id)}');
+                       '&objectId=${Uri.encodeComponent(obj.id)}');
       }
     }
     return url;