Fix reuse of <ref> elements

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 46f1ef555d74d310fe5e7e4aebe47ca221448eee..da2735eb41691efce1e933ea1790f161f887fe8d 100644
--- a/runtime/observatory/lib/src/elements/observatory_element.dart
+++ b/runtime/observatory/lib/src/elements/observatory_element.dart
@@ -164,7 +164,18 @@ class ObservatoryElement extends PolymerElement {
 
   void clearShadowRoot() {
     // Remove all non-style elements.
-    shadowRoot.children.removeWhere((e) => e is! StyleElement);
+    // Have to do the following because removeWhere doesn't work on DOM child
+    // node lists. i.e. removeWhere((e) => e is! StyleElement);
+    var styleElements = [];
+    for (var child in shadowRoot.children) {
+      if (child is StyleElement) {
+        styleElements.add(child);
+      }
+    }
+    shadowRoot.children.clear();
+    for (var style in styleElements) {
+      shadowRoot.children.add(style);
+    }
   }
 
   void insertTextSpanIntoShadowRoot(String text) {