fix #28988, remove throw on Dart1 incompatible is-checks for dartdevc

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

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This library adapts ES6 generators to implement Dart's async/await.
 /// It's designed to interact with Dart's Future/Stream and follow Dart
 /// async/await semantics.
 /// See https://github.com/dart-lang/sdk/issues/27315 for ideas on
 /// reconciling Dart's Future and ES6 Promise.
 /// Inspired by `co`: https://github.com/tj/co/blob/master/index.js, which is a
@@ skipping 44 matching lines @@
     // Wraps if future is not a native Future.
     if (_getRawClassType(future) !== _FutureType) {
       future = $Future.value(future);
     }
     // Chain the Future so `await` receives the Future's value.
     return future.then($dynamic)(onValue, {onError: onError});
   }
   let result = FutureT.microtask(function() {
     iter = $gen.apply(null, $args)[Symbol.iterator]();
     var result = onValue();
-    if ($strongInstanceOf(result, FutureT) == null) {
+    if ($isSubtype($getReifiedType(result), FutureT) == null) {
       // Chain the Future<dynamic> to a Future<T> to produce the correct
       // final type.
       return result.then($T)((x) => x, {onError: onError});
     } else {
       return result;
     }
   });
   // TODO(jmesserly): optimize this further.
   _FutureType = _getRawClassType(result);
   return result;  
@@ skipping 161 matching lines @@
       }
       if (!this.controller.hasListener) return;
       this.controller.addError(error, stackTrace);
     }
   }
 ''');
 
 /// Returns a Stream of T implemented by an async* function.
 asyncStar(gen, T, @rest args) => JS('', 'new #(#, #, #).controller.stream',
     _AsyncStarStreamController, gen, T, args);