Bug 1734700 - Use the IO event queue for IOUtils background tasks, r=KrisWright

Differential Revision: https://phabricator.services.mozilla.com/D128311

dom/system/IOUtils.cpp

@@ -1597,14 +1597,20 @@ template <typename OkT, typename Fn>
 RefPtr<IOUtils::IOPromise<OkT>> IOUtils::EventQueue::Dispatch(Fn aFunc) {
   MOZ_RELEASE_ASSERT(mBackgroundEventTarget);
 
-  return InvokeAsync(
-      mBackgroundEventTarget, __func__, [func = std::move(aFunc)]() {
-        Result<OkT, IOError> result = func();
-        if (result.isErr()) {
-          return IOPromise<OkT>::CreateAndReject(result.unwrapErr(), __func__);
-        }
-        return IOPromise<OkT>::CreateAndResolve(result.unwrap(), __func__);
-      });
+  auto promise =
+      MakeRefPtr<typename IOUtils::IOPromise<OkT>::Private>(__func__);
+  mBackgroundEventTarget->Dispatch(
+      NS_NewRunnableFunction("IOUtils::EventQueue::Dispatch",
+                             [promise, func = std::move(aFunc)] {
+                               Result<OkT, IOError> result = func();
+                               if (result.isErr()) {
+                                 promise->Reject(result.unwrapErr(), __func__);
+                               } else {
+                                 promise->Resolve(result.unwrap(), __func__);
+                               }
+                             }),
+      NS_DISPATCH_EVENT_MAY_BLOCK);
+  return promise;
 };
 
 Result<already_AddRefed<nsIAsyncShutdownClient>, nsresult>