Add functions to host config

add getCurrentEventStartTime and scheduleTransitionCallbacks to host configs

packages/react-art/src/ReactARTHostConfig.js

@@ -451,3 +451,11 @@ export function preparePortalMount(portalInstance: any): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function getCurrentEventStartTime() {
+  // noop
+}
+
+export function scheduleTransitionCallbacks(callback, pendingTransitions) {
+  // noop
+}

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

@@ -70,6 +70,11 @@ import {HostComponent, HostText} from 'react-reconciler/src/ReactWorkTags';
 import {listenToAllSupportedEvents} from '../events/DOMPluginEventSystem';
 
 import {DefaultEventPriority} from 'react-reconciler/src/ReactEventPriorities';
+import {
+  now,
+  scheduleCallback,
+  IdlePriority,
+} from 'react-reconciler/src/Scheduler';
 
 export type Type = string;
 export type Props = {
@@ -1241,3 +1246,27 @@ export function setupIntersectionObserver(
     },
   };
 }
+
+export function getCurrentEventStartTime(): number {
+  const event = window.event;
+  if (event === undefined) {
+    return now();
+  }
+  return event.timeStamp;
+}
+
+// TODO(luna) Fix this because rAF doesn't actually do
+// what you want here
+export function scheduleTransitionCallbacks(
+  callback: (Array<{}>, endTime: number) => void,
+  // TODO(luna) Figure out type of this
+  pendingTransitions: Array<{}>,
+): void {
+  window.requestAnimationFrame(() => {
+    const endTime = now();
+
+    scheduleCallback(IdlePriority, () => {
+      callback(pendingTransitions, endTime);
+    });
+  });
+}

packages/react-native-renderer/src/ReactFabricHostConfig.js

@@ -525,3 +525,11 @@ export function preparePortalMount(portalInstance: Instance): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function getCurrentEventStartTime() {
+  // noop
+}
+
+export function scheduleTransitionCallbacks(callback, pendingTransitions) {
+  // noop
+}

packages/react-native-renderer/src/ReactNativeHostConfig.js

@@ -513,3 +513,11 @@ export function preparePortalMount(portalInstance: Instance): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function getCurrentEventStartTime() {
+  // noop
+}
+
+export function scheduleTransitionCallbacks(callback, pendingTransitions) {
+  // noop
+}

packages/react-noop-renderer/src/createReactNoop.js

@@ -466,6 +466,12 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     },
 
     detachDeletedInstance() {},
+
+    getCurrentEventStartTime() {
+      return Scheduler.unstable_now();
+    },
+
+    scheduleTransitionCallbacks(callback, pendingTransitions) {},
   };
 
   const hostConfig = useMutation

packages/react-reconciler/src/forks/ReactFiberHostConfig.custom.js

@@ -189,3 +189,11 @@ export const didNotFindHydratableTextInstance =
 export const didNotFindHydratableSuspenseInstance =
   $$$hostConfig.didNotFindHydratableSuspenseInstance;
 export const errorHydratingContainer = $$$hostConfig.errorHydratingContainer;
+
+// -------------------
+//      Transition Tracing
+//     (optional)
+// -------------------
+export const getCurrentEventStartTime = $$$hostConfig.getCurrentEventStartTime;
+export const scheduleTransitionCallbacks =
+  $$$hostConfig.scheduleTransitionCallbacks;

packages/react-test-renderer/src/ReactTestHostConfig.js

@@ -314,3 +314,11 @@ export function getInstanceFromScope(scopeInstance: Object): null | Object {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function getCurrentEventStartTime() {
+  // noop
+}
+
+export function scheduleTransitionCallbacks(callback, pendingTransitions) {
+  // noop
+}