Support FutureOr<T> in the VM (fixes #28010).

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index afa023ae0713741b21a16bc18e0d1aa10310b597..923526885ecea9685b32b527aa03bcd12b6b9592 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -12045,6 +12045,13 @@ void Parser::ResolveType(ClassFinalizer::FinalizationKind finalization,
         parameterized_type.set_signature(
             Function::Handle(Z, resolved_type_class.signature_function()));
       }
+      // Replace FutureOr<T> type of async library with dynamic.
+      if ((resolved_type_class.library() == Library::AsyncLibrary()) &&
+          (resolved_type_class.Name() == Symbols::FutureOr().raw())) {
+        parameterized_type.set_type_class(
+            Class::Handle(Object::dynamic_class()));
+        parameterized_type.set_arguments(Object::null_type_arguments());
+      }
     } else if (finalization >= ClassFinalizer::kCanonicalize) {
       ClassFinalizer::FinalizeMalformedType(
           Error::Handle(Z),  // No previous error.