Clarify presentation of the target in retaining paths.

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

Index: runtime/observatory/lib/src/elements/unknown_ref.dart
diff --git a/runtime/observatory/lib/src/elements/unknown_ref.dart b/runtime/observatory/lib/src/elements/unknown_ref.dart
index 3165877759ddc060e03f6f9bfcd2a1c205d169c1..d5723c447d0ee32c44eea6ac1177b82777c59335 100644
--- a/runtime/observatory/lib/src/elements/unknown_ref.dart
+++ b/runtime/observatory/lib/src/elements/unknown_ref.dart
@@ -52,6 +52,7 @@ class UnknownObjectRefElement extends HtmlElement implements Renderable {
   void render() {
     children = [
       new AnchorElement(href: Uris.inspect(_isolate, object: _obj))
+        ..classes = ['emphasize']
         ..text = _obj.vmType
     ];
   }