Enable Try Dart to run on IE11.

site/try/src/settings.dart

Index: site/try/src/settings.dart
===================================================================
--- site/try/src/settings.dart	(revision 39366)
+++ site/try/src/settings.dart	(working copy)
@@ -95,6 +95,12 @@
 
 const BooleanUserOption live = const BooleanUserOption('live', isHidden: true);
 
+const BooleanUserOption alwaysRunInIframe =
+    const BooleanUserOption('alwaysRunInIframe', isHidden: true);
+
+const BooleanUserOption communicateViaBlobs =
+    const BooleanUserOption('communicateViaBlobs', isHidden: true);
+
 const List<UserOption> options = const <UserOption>[
     _alwaysRunInWorker,
     _verboseCompiler,
@@ -108,4 +114,6 @@
     _codeFont,
     _theme,
     _currentSample,
+    alwaysRunInIframe,
+    communicateViaBlobs,
   ];