[scheduler] 4/n Allow splitting out schedule in fb-www, prepare to fix polyfill issue internally (#12900)

* Use local references to global things inside 'scheduler'

**what is the change?:**
See title

**why make this change?:**
We want to avoid initially calling one version of an API and then later
accessing a polyfilled version.

**test plan:**
Run existing tests.

* Shim ReactScheduler for www

**what is the change?:**
In 'www' we want to reference the separate build of ReactScheduler,
which allows treating it as a separate module internally.

**why make this change?:**
We need to require the ReactScheduler before our rAF polyfill activates,
in order to customize which custom behaviors we want.

This is also a step towards being able to experiment with using it
outside of React.

**test plan:**
Ran tests, ran the build, and ran `test-build`.

* Generate a bundle for fb-www

**what is the change?:**
See title

**why make this change?:**
Splitting out the 'schedule' module allows us to load it before
polyfills kick in for rAF and other APIs.

And long term we want to split this into a separate module anyway, this
is a step towards that.

**test plan:**
I'll run the sync next week and verify that this all works. :)

* ran prettier

* fix rebase issues

* Change names of variables used for holding globals

Author: flarnie

packages/react-art/src/ReactARTHostConfig.js

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import * as ReactScheduler from 'react-scheduler';
+import * as ReactScheduler from 'shared/ReactScheduler';
 import Transform from 'art/core/transform';
 import Mode from 'art/modes/current';
 import invariant from 'fbjs/lib/invariant';

packages/react-dom/src/client/ReactDOMHostConfig.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import * as ReactScheduler from 'react-scheduler';
+import * as ReactScheduler from 'shared/ReactScheduler';
 
 import * as ReactDOMComponentTree from './ReactDOMComponentTree';
 import * as ReactDOMFiberComponent from './ReactDOMFiberComponent';

packages/react-scheduler/src/ReactScheduler.js

@@ -44,13 +44,21 @@ export type CallbackIdType = CallbackConfigType;
 import requestAnimationFrameForReact from 'shared/requestAnimationFrameForReact';
 import ExecutionEnvironment from 'fbjs/lib/ExecutionEnvironment';
 
+// We capture a local reference to any global, in case it gets polyfilled after
+// this module is initially evaluated.
+// We want to be using a consistent implementation.
+const Date = global.Date;
+const setTimeout = global.setTimeout;
+const clearTimeout = global.clearTimeout;
+
 const hasNativePerformanceNow =
   typeof performance === 'object' && typeof performance.now === 'function';
 
 let now;
 if (hasNativePerformanceNow) {
+  const Performance = performance;
   now = function() {
-    return performance.now();
+    return Performance.now();
   };
 } else {
   now = function() {
@@ -224,7 +232,7 @@ if (!ExecutionEnvironment.canUseDOM) {
   };
   // Assumes that we have addEventListener in this environment. Might need
   // something better for old IE.
-  window.addEventListener('message', idleTick, false);
+  global.addEventListener('message', idleTick, false);
 
   const animationTick = function(rafTime) {
     isAnimationFrameScheduled = false;

packages/shared/ReactScheduler.js

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+'use strict';
+import {
+  now,
+  scheduleWork,
+  cancelScheduledWork,
+} from 'react-scheduler/src/ReactScheduler';
+
+export {now, scheduleWork, cancelScheduledWork};

packages/shared/forks/ReactScheduler.www.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+const {now, scheduleWork, cancelScheduledWork} = require('customSchedule');
+
+export {now, scheduleWork, cancelScheduledWork};

packages/shared/requestAnimationFrameForReact.js

@@ -12,6 +12,11 @@
 import ExecutionEnvironment from 'fbjs/lib/ExecutionEnvironment';
 import warning from 'fbjs/lib/warning';
 
+// We capture a local reference to any global, in case it gets polyfilled after
+// this module is initially evaluated.
+// We want to be using a consistent implementation.
+const requestAnimationFrame = global.requestAnimationFrame;
+
 if (__DEV__) {
   if (
     ExecutionEnvironment.canUseDOM &&

scripts/rollup/bundles.js

@@ -371,7 +371,14 @@ const bundles = [
   /******* React Scheduler (experimental) *******/
   {
     label: 'react-scheduler',
-    bundleTypes: [NODE_DEV, NODE_PROD, UMD_DEV, UMD_PROD],
+    bundleTypes: [
+      UMD_DEV,
+      UMD_PROD,
+      NODE_DEV,
+      NODE_PROD,
+      FB_WWW_DEV,
+      FB_WWW_PROD,
+    ],
     moduleType: ISOMORPHIC,
     entry: 'react-scheduler',
     global: 'ReactScheduler',

scripts/rollup/forks.js

@@ -79,6 +79,7 @@ const forks = Object.freeze({
   },
 
   // This logic is forked on www to use the 'acrossTransitions' version.
+  // This will be removed soon, see internal task T29442940
   'shared/requestAnimationFrameForReact': (bundleType, entry) => {
     switch (bundleType) {
       case FB_WWW_DEV:
@@ -89,6 +90,16 @@ const forks = Object.freeze({
     }
   },
 
+  'shared/ReactScheduler': (bundleType, entry) => {
+    switch (bundleType) {
+      case FB_WWW_DEV:
+      case FB_WWW_PROD:
+        return 'shared/forks/ReactScheduler.www.js';
+      default:
+        return null;
+    }
+  },
+
   // This logic is forked on www to blacklist warnings.
   'shared/lowPriorityWarning': (bundleType, entry) => {
     switch (bundleType) {