Removed const from classes arrays in Observatory

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

Index: runtime/observatory/lib/src/elements/sentinel_view.dart
diff --git a/runtime/observatory/lib/src/elements/sentinel_view.dart b/runtime/observatory/lib/src/elements/sentinel_view.dart
index 4fcc00d64c1de279fe1f4ddec021efb3089ce222..8fff0d57a91e4569fdd74c6fb8851e77e9e81014 100644
--- a/runtime/observatory/lib/src/elements/sentinel_view.dart
+++ b/runtime/observatory/lib/src/elements/sentinel_view.dart
@@ -85,7 +85,7 @@ class SentinelViewElement extends HtmlElement implements Renderable {
           new NavMenuElement('sentinel', last: true, queue: _r.queue),
           new NavNotifyElement(_notifications, queue: _r.queue)
         ],
-      new DivElement()..classes = const ['content-centered-big']
+      new DivElement()..classes = ['content-centered-big']
         ..children = [
           new HeadingElement.h2()
             ..text = 'Sentinel: #{_sentinel.valueAsString}',