move post paint logic to another module and use it in the work loop

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

@@ -83,7 +83,6 @@ import {
   supportsMicrotasks,
   errorHydratingContainer,
   scheduleMicrotask,
-  requestPostPaintCallback,
 } from './ReactFiberHostConfig';
 
 import {
@@ -261,6 +260,7 @@ import {
   suspendedThenableDidResolve,
   isTrackingSuspendedThenable,
 } from './ReactFiberWakeable.new';
+import {schedulPostPaintCallback} from './ReactPostPaintCallback';
 
 const ceil = Math.ceil;
 
@@ -2653,7 +2653,7 @@ function commitRootImpl(
     // and then call the callback via the correct end time.
     const prevRootTransitionCallbacks = root.transitionCallbacks;
     if (prevRootTransitionCallbacks !== null) {
-      requestPostPaintCallback(endTime => {
+      schedulPostPaintCallback(endTime => {
         const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
         if (prevPendingTransitionCallbacks !== null) {
           currentPendingTransitionCallbacks = null;

packages/react-reconciler/src/ReactPostPaintCallback.js

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+import {requestPostPaintCallback} from './ReactFiberHostConfig';
+
+let postPaintCallbackScheduled = false;
+let callbacks = [];
+
+export function schedulPostPaintCallback(callback) {
+  callbacks.push(callback);
+  if (!postPaintCallbackScheduled) {
+    postPaintCallbackScheduled = true;
+    requestPostPaintCallback(endTime => {
+      for (let i = 0; i < callbacks.length; i++) {
+        callbacks[i](endTime);
+      }
+      postPaintCallbackScheduled = false;
+      callbacks = [];
+    });
+  }
+}