test(transpiler): add spec for instanceof

tools/transpiler/spec/instance_of_spec.js

@@ -0,0 +1,11 @@
+import {describe, it, expect} from 'test_lib/test_lib';
+
+class Foo {}
+
+export function main() {
+  describe('instanceof', function() {
+    it('should work', function() {
+      expect(new Foo() instanceof Foo);
+    });
+  });
+}