Expand ignore whitelist to include FutureOr

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart

Index: pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
index ef253e0ca7c7956dce3b139a6d4af296e592e13e..4475a546052da9e2686174fc12db9158f1e385ac 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
@@ -749,8 +749,11 @@ _isSubtype(t1, t2, isCovariant) => JS(
     // t1 <: (Future<A> | A) iff t1 <: Future<A> or t1 <: A
     let t2TypeArg = $getGenericArgs($t2)[0];
     var t2Future = ${getGenericClass(Future)}(t2TypeArg);
-    return $_isSubtype($t1, t2Future, $isCovariant) ||
-        $_isSubtype($t1, t2TypeArg, $isCovariant);
+    let s1 = $_isSubtype($t1, t2Future, $isCovariant);
+    let s2 = $_isSubtype($t1, t2TypeArg, $isCovariant);
+    if (s1 === true || s2 === true) return true;
+    if (s1 === null || s2 === null) return null;
+    return false;
   }
 
   // "Traditional" name-based subtype check.  Avoid passing