restore FutureOr cast failure ignore

pkg/dev_compiler/lib/js/common/dart_sdk.js

Index: pkg/dev_compiler/lib/js/common/dart_sdk.js
diff --git a/pkg/dev_compiler/lib/js/common/dart_sdk.js b/pkg/dev_compiler/lib/js/common/dart_sdk.js
index 92c8205dadb893e5f21ca19e652ab74ab9186270..9bd0c6f3589251019c243fa721eca1daac1227b3 100644
--- a/pkg/dev_compiler/lib/js/common/dart_sdk.js
+++ b/pkg/dev_compiler/lib/js/common/dart_sdk.js
@@ -20414,11 +20414,11 @@ async.FutureOr$ = dart.generic(T => {
   };
   FutureOr.as = function as_FutureOr(o) {
     if (o == null || T.is(o) || FutureOfT().is(o)) return o;
-    return dart.castError(o, this, false);
+    return dart.as(o, this, false);
   };
   FutureOr._check = function check_FutureOr(o) {
     if (o == null || T.is(o) || FutureOfT().is(o)) return o;
-    return dart.castError(o, this, true);
+    return dart.as(o, this, true);
   };
   return FutureOr;
 });