Replace old Fiber Scheduler with new one (#15387)

The new Fiber Scheduler has been running in Facebook for several days
without issues. Let's switch to it.

package.json

@@ -102,7 +102,6 @@
  "test": "cross-env NODE_ENV=development jest --config ./scripts/jest/config.source.js",
  "test-persistent": "cross-env NODE_ENV=development jest --config ./scripts/jest/config.source-persistent.js",
  "test-fire": "cross-env NODE_ENV=development jest --config ./scripts/jest/config.source-fire.js",
- "test-new-scheduler": "cross-env NODE_ENV=development jest --config ./scripts/jest/config.source-new-scheduler.js",
  "test-prod": "cross-env NODE_ENV=production jest --config ./scripts/jest/config.source.js",
  "test-fire-prod": "cross-env NODE_ENV=production jest --config ./scripts/jest/config.source-fire.js",
  "test-prod-build": "yarn test-build-prod",

packages/react-dom/src/__tests__/ReactDOMHooks-test.internal.js → packages/react-dom/src/__tests__/ReactDOMHooks-test.js

@@ -9,8 +9,6 @@
 
 'use strict';
 
-let ReactFeatureFlags;
-let enableNewScheduler;
 let React;
 let ReactDOM;
 let Scheduler;
@@ -21,8 +19,6 @@ describe('ReactDOMHooks', () => {
  beforeEach(() => {
  jest.resetModules();
 
- ReactFeatureFlags = require('shared/ReactFeatureFlags');
- enableNewScheduler = ReactFeatureFlags.enableNewScheduler;
  React = require('react');
  ReactDOM = require('react-dom');
  Scheduler = require('scheduler');
@@ -101,30 +97,15 @@ describe('ReactDOMHooks', () => {
  }
 
  ReactDOM.render(<Foo />, container);
-
- if (enableNewScheduler) {
- // The old behavior was accidental; in the new scheduler, flushing passive
- // effects also flushes synchronous work, even inside batchedUpdates.
- ReactDOM.unstable_batchedUpdates(() => {
- _set(0); // Forces the effect to be flushed
- expect(otherContainer.textContent).toBe('A');
- ReactDOM.render(<B />, otherContainer);
- expect(otherContainer.textContent).toBe('A');
- });
- expect(otherContainer.textContent).toBe('B');
- expect(calledA).toBe(true);
- expect(calledB).toBe(true);
- } else {
- ReactDOM.unstable_batchedUpdates(() => {
- _set(0); // Forces the effect to be flushed
- expect(otherContainer.textContent).toBe('');
- ReactDOM.render(<B />, otherContainer);
- expect(otherContainer.textContent).toBe('');
- });
- expect(otherContainer.textContent).toBe('B');
- expect(calledA).toBe(false); // It was in a batch
- expect(calledB).toBe(true);
- }
+ ReactDOM.unstable_batchedUpdates(() => {
+ _set(0); // Forces the effect to be flushed
+ expect(otherContainer.textContent).toBe('A');
+ ReactDOM.render(<B />, otherContainer);
+ expect(otherContainer.textContent).toBe('A');
+ });
+ expect(otherContainer.textContent).toBe('B');
+ expect(calledA).toBe(true);
+ expect(calledB).toBe(true);
  });
 
  it('should not bail out when an update is scheduled from within an event handler', () => {