Fix DDC cross-window JS interop on FireFox.

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 9e510b10195c35269d28327630d402f14d3f4ad1..deef7b3bf4b2eabfa9d4156aa2a5bb79a3064b53 100644
--- a/pkg/dev_compiler/lib/js/common/dart_sdk.js
+++ b/pkg/dev_compiler/lib/js/common/dart_sdk.js
@@ -52899,7 +52899,7 @@
   });
   js.JsArray = JsArray();
   js._isBrowserType = function(o) {
-    return o instanceof Blob || o instanceof Event || window.KeyRange && o instanceof KeyRange || window.IDBKeyRange && o instanceof IDBKeyRange || o instanceof ImageData || o instanceof Node || window.Int8Array && o instanceof Int8Array.__proto__ || o instanceof Window;
+    return o instanceof Object && (o instanceof Blob || o instanceof Event || window.KeyRange && o instanceof KeyRange || window.IDBKeyRange && o instanceof IDBKeyRange || o instanceof ImageData || o instanceof Node || window.Int8Array && o instanceof Int8Array.__proto__ || o instanceof Window);
   };
   dart.fn(js._isBrowserType, dynamicTobool$());
   const _dartObj = Symbol('_dartObj');