Removed const from classes arrays in Observatory

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

Index: runtime/observatory/lib/src/elements/field_view.dart
diff --git a/runtime/observatory/lib/src/elements/field_view.dart b/runtime/observatory/lib/src/elements/field_view.dart
index f6325ee671d8055196145488578293d0fb90c4c8..9fe7b82d2b7dca1d63b14521fef206242951a87e 100644
--- a/runtime/observatory/lib/src/elements/field_view.dart
+++ b/runtime/observatory/lib/src/elements/field_view.dart
@@ -155,7 +155,7 @@ class FieldViewElement extends HtmlElement implements Renderable {
     children = [
       new NavBarElement(queue: _r.queue)
         ..children = _createMenu(),
-      new DivElement()..classes = const ['content-centered-big']
+      new DivElement()..classes = ['content-centered-big']
         ..children = [
           new HeadingElement.h2()..text = '$header ${field.name}',
           new HRElement(),