Prevent changes to hidden properties from being observable via Object.observe

test/cctest/test-object-observe.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 702 matching lines @@
     instance->Set(String::New("foo"), String::New("bar"));
     CompileRun("");  // trigger delivery
     const RecordExpectation expected_records2[] = {
       { instance, "new", "5", Handle<Value>() },
       { instance, "new", "foo", Handle<Value>() }
     };
     EXPECT_RECORDS(CompileRun("records2"), expected_records2);
   }
   CHECK(CompileRun("records")->IsNull());
 }
+
+
+TEST(HiddenPropertiesLeakage) {
+  HarmonyIsolate isolate;
+  HandleScope scope(isolate.GetIsolate());
+  LocalContext context(isolate.GetIsolate());
+  CompileRun("var obj = {};"
+             "var records = null;"
+             "var observer = function(r) { records = r };"
+             "Object.observe(obj, observer);");
+  Handle<Value> obj = context->Global()->Get(String::New("obj"));
+  Handle<Object>::Cast(obj)->SetHiddenValue(String::New("foo"), Null());
+  CompileRun("");  // trigger delivery
+  CHECK(CompileRun("records")->IsNull());
+}