Bug 1189822 part 1. Switch DOMProxyHandler::EnsureExpandoObject to using normal wrapper preservation instead of RegisterDOMExpandoObject. r=peterv

dom/bindings/DOMJSProxyHandler.cpp

@@ -76,17 +76,9 @@ DOMProxyHandler::ClearExternalRefsForWrapperRelease(JSObject* obj)
 {
   MOZ_ASSERT(IsDOMProxy(obj), "expected a DOM proxy object");
   JS::Value v = js::GetProxyPrivate(obj);
-  if (v.isUndefined()) {
-    // No expando.
-    return;
-  }
-
-  // See EnsureExpandoObject for the work we're trying to undo here.
-
-  if (v.isObject()) {
-    // Drop us from the DOM expando hashtable.  Don't worry about clearing our
-    // slot reference to the expando; we're about to die anyway.
-    xpc::ObjectScope(obj)->RemoveDOMExpandoObject(obj);
+  if (v.isUndefined() || v.isObject()) {
+    // No expando, or an expando that we reference from our slot anyway, so
+    // don't have to clear state for.
     return;
   }
 
@@ -109,7 +101,6 @@ DOMProxyHandler::GetAndClearExpandoObject(JSObject* obj)
 
   if (v.isObject()) {
     js::SetProxyPrivate(obj, UndefinedValue());
-    xpc::ObjectScope(obj)->RemoveDOMExpandoObject(obj);
   } else {
     js::ExpandoAndGeneration* expandoAndGeneration =
       static_cast<js::ExpandoAndGeneration*>(v.toPrivate());
@@ -166,18 +157,13 @@ DOMProxyHandler::EnsureExpandoObject(JSContext* cx, JS::Handle<JSObject*> obj)
   nsISupports* native = UnwrapDOMObject<nsISupports>(obj);
   nsWrapperCache* cache;
   CallQueryInterface(native, &cache);
-  if (expandoAndGeneration) {
-    cache->PreserveWrapper(native);
-    expandoAndGeneration->expando.setObject(*expando);
+  cache->PreserveWrapper(native);
 
+  if (expandoAndGeneration) {
+    expandoAndGeneration->expando.setObject(*expando);
     return expando;
   }
 
-  if (!xpc::ObjectScope(obj)->RegisterDOMExpandoObject(obj)) {
-    return nullptr;
-  }
-
-  cache->SetPreservingWrapper(true);
   js::SetProxyPrivate(obj, ObjectValue(*expando));
 
   return expando;