Removed Polymer from Observatory deps

packages/web_components/lib/polyfill.dart

Index: packages/web_components/lib/polyfill.dart
diff --git a/packages/web_components/lib/polyfill.dart b/packages/web_components/lib/polyfill.dart
index 6e7bbd95e7acfa214a3362bbc79f297849bc032a..e225e22db92820c15ff867c2c98dc099fd8b1593 100644
--- a/packages/web_components/lib/polyfill.dart
+++ b/packages/web_components/lib/polyfill.dart
@@ -38,7 +38,7 @@ bool get _isReady {
   if (customElements == null) {
     // Return true if native document.register, otherwise false.
     // (Maybe the polyfill isn't loaded yet. Wait for it.)
-    return document.supportsRegister;
+    return document.supportsRegisterElement;
   }
 
   return customElements['ready'] == true;