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

test/cctest/test-object-observe.cc

Index: test/cctest/test-object-observe.cc
diff --git a/test/cctest/test-object-observe.cc b/test/cctest/test-object-observe.cc
index a9f840e7adc7f0d0b48ed3a600baed1698ce64b2..b4488a603a981a9e420abda0fc00f66e28c4b4de 100644
--- a/test/cctest/test-object-observe.cc
+++ b/test/cctest/test-object-observe.cc
@@ -720,3 +720,18 @@ TEST(AccessCheckDisallowApiModifications) {
   }
   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());
+}