Removed polymer & mirror from Observatory

runtime/observatory/lib/src/app/page.dart

Index: runtime/observatory/lib/src/app/page.dart
diff --git a/runtime/observatory/lib/src/app/page.dart b/runtime/observatory/lib/src/app/page.dart
index cdcb45716cd7e0864d4bc9967c0fef54ed25b118..9b8705e2ab08f1cb64f600e5a24adebce9def3cb 100644
--- a/runtime/observatory/lib/src/app/page.dart
+++ b/runtime/observatory/lib/src/app/page.dart
@@ -48,11 +48,10 @@ RetainingPathRepository _retainingPathRepository
 /// one page will be the current page. Pages are registered at startup.
 /// When the user navigates within the application, each page is asked if it
 /// can handle the current location, the first page to say yes, wins.
-abstract class Page extends Observable {
+abstract class Page {
   final ObservatoryApplication app;
-  final ObservableMap<String, String> internalArguments =
-      new ObservableMap<String, String>();
-  @observable HtmlElement element;
+  final Map<String, String> internalArguments = <String, String>{};
+  HtmlElement element;
 
   Page(this.app);