Add PressabilityPerformanceEventEmitter

Summary:
Add PressabilityPerformanceEventEmitter which allows product code / infrastructure to subscribe to touch-related performance events.

Changelog: [Added][JS] Product/infra can subscribe to Pressability touch events for telemetry purposes

Reviewed By: fkgozali

Differential Revision: D27034835

fbshipit-source-id: e62811f641994b9eadb5cdd7391e806b6cce479a

Author: JoshuaGross

Libraries/Pressability/Pressability.js

@@ -18,6 +18,8 @@ import type {
   PressEvent,
   MouseEvent,
 } from '../Types/CoreEventTypes';
+import PressabilityPerformanceEventEmitter from './PressabilityPerformanceEventEmitter.js';
+import {type PressabilityTouchSignal as TouchSignal} from './PressabilityTypes.js';
 import Platform from '../Utilities/Platform';
 import UIManager from '../ReactNative/UIManager';
 import type {HostComponent} from '../Renderer/shims/ReactNativeTypes';
@@ -174,15 +176,6 @@ type TouchState =
   | 'RESPONDER_ACTIVE_LONG_PRESS_OUT'
   | 'ERROR';
 
-type TouchSignal =
-  | 'DELAY'
-  | 'RESPONDER_GRANT'
-  | 'RESPONDER_RELEASE'
-  | 'RESPONDER_TERMINATED'
-  | 'ENTER_PRESS_RECT'
-  | 'LEAVE_PRESS_RECT'
-  | 'LONG_PRESS_DETECTED';
-
 const Transitions = Object.freeze({
   NOT_RESPONDER: {
     DELAY: 'ERROR',
@@ -630,6 +623,13 @@ export default class Pressability {
         : '<<host component>>',
     );
     if (prevState !== nextState) {
+      PressabilityPerformanceEventEmitter.emitEvent(() => {
+        return {
+          signal,
+          touchDelayMs: Date.now() - event.nativeEvent.timestamp,
+        };
+      });
+
       this._performTransitionSideEffects(prevState, nextState, signal, event);
       this._touchState = nextState;
     }

Libraries/Pressability/PressabilityPerformanceEventEmitter.js

@@ -0,0 +1,47 @@
+/**
+ * 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 strict-local
+ * @format
+ */
+
+import {type PressabilityTouchSignal as TouchSignal} from './PressabilityTypes.js';
+
+export type PressabilityPerformanceEvent = $ReadOnly<{|
+  signal: TouchSignal,
+  touchDelayMs: number,
+|}>;
+export type PressabilityPerformanceEventListener = PressabilityPerformanceEvent => void;
+
+class PressabilityPerformanceEventEmitter {
+  _listeners: Array<PressabilityPerformanceEventListener> = [];
+
+  constructor() {}
+
+  addListener(listener: PressabilityPerformanceEventListener): void {
+    this._listeners.push(listener);
+  }
+
+  removeListener(listener: PressabilityPerformanceEventListener): void {
+    const index = this._listeners.indexOf(listener);
+    if (index > -1) {
+      this._listeners.splice(index, 1);
+    }
+  }
+
+  emitEvent(constructEvent: () => PressabilityPerformanceEvent): void {
+    if (this._listeners.length === 0) {
+      return;
+    }
+
+    const event = constructEvent();
+    this._listeners.forEach(listener => listener(event));
+  }
+}
+
+const PressabilityPerformanceEventEmitterSingleton: PressabilityPerformanceEventEmitter = new PressabilityPerformanceEventEmitter();
+
+export default PressabilityPerformanceEventEmitterSingleton;

Libraries/Pressability/PressabilityTypes.js

@@ -0,0 +1,18 @@
+/**
+ * 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 strict-local
+ * @format
+ */
+
+export type PressabilityTouchSignal =
+  | 'DELAY'
+  | 'RESPONDER_GRANT'
+  | 'RESPONDER_RELEASE'
+  | 'RESPONDER_TERMINATED'
+  | 'ENTER_PRESS_RECT'
+  | 'LEAVE_PRESS_RECT'
+  | 'LONG_PRESS_DETECTED';