Bug 1605801 - FetchReadableStreamReadDataArray should be a rooted dictionary, r=bzbarsky

Differential Revision: https://phabricator.services.mozilla.com/D58176

--HG--
extra : moz-landing-system : lando

dom/fetch/FetchStreamReader.cpp

@@ -253,15 +253,14 @@ void FetchStreamReader::ResolvedCallback(JSContext* aCx,
     return;
   }
 
-  UniquePtr<FetchReadableStreamReadDataArray> value(
-      new FetchReadableStreamReadDataArray);
-  if (!value->Init(aCx, aValue) || !value->mValue.WasPassed()) {
+  RootedDictionary<FetchReadableStreamReadDataArray> value(aCx);
+  if (!value.Init(aCx, aValue) || !value.mValue.WasPassed()) {
     JS_ClearPendingException(aCx);
     CloseAndRelease(aCx, NS_ERROR_DOM_INVALID_STATE_ERR);
     return;
   }
 
-  Uint8Array& array = value->mValue.Value();
+  Uint8Array& array = value.mValue.Value();
   array.ComputeLengthAndData();
   uint32_t len = array.Length();