React Native: Touch Instrumentation Interface (#21024)

Author: yungsters

packages/react-native-renderer/src/legacy-events/ResponderTouchHistoryStore.js

@@ -184,8 +184,21 @@ function printTouchBank(): string {
   return printed;
 }
 
+let instrumentationCallback: ?(string, TouchEvent) => void;
+
 const ResponderTouchHistoryStore = {
+  /**
+   * Registers a listener which can be used to instrument every touch event.
+   */
+  instrument(callback: (string, TouchEvent) => void): void {
+    instrumentationCallback = callback;
+  },
+
   recordTouchTrack(topLevelType: string, nativeEvent: TouchEvent): void {
+    if (instrumentationCallback != null) {
+      instrumentationCallback(topLevelType, nativeEvent);
+    }
+
     if (isMoveish(topLevelType)) {
       nativeEvent.changedTouches.forEach(recordTouchMove);
     } else if (isStartish(topLevelType)) {