Extract feature detection as an utilitiy module

Summary:
Changelog: [Internal]

This diff only extracted the `isNativeFunction` used in `setUpTimers`
into the `FeatureDetection` utility, but later we will add more functions
in it and reuse them in other places.

Reviewed By: RSNara

Differential Revision: D29986750

fbshipit-source-id: 6e48e38d92ceccb35eead3c52e00e1eecb81b5b0

Libraries/Core/setUpTimers.js

@@ -11,6 +11,7 @@
 'use strict';
 
 const {polyfillGlobal} = require('../Utilities/PolyfillFunctions');
+const {isNativeFunction} = require('../Utilities/FeatureDetection');
 
 if (__DEV__) {
   if (typeof global.Promise !== 'function') {
@@ -23,14 +24,7 @@ const hasHermesPromiseQueuedToJSVM =
   global?.HermesInternal?.hasPromise?.() &&
   global?.HermesInternal?.useEngineQueue?.();
 
-// An util function to tell whether a function is provided natively by calling
-// the `toString` and check if the result includes `[native code]` in it.
-// N.B. a polyfill can fake this behavior but they usually won't. Hence this
-// is usually good enough for our purpose.
-const isNativeFunction = f =>
-  typeof f === 'function' && f.toString().indexOf('[native code]') > -1;
 const hasNativePromise = isNativeFunction(Promise);
-
 const hasPromiseQueuedToJSVM = hasNativePromise || hasHermesPromiseQueuedToJSVM;
 
 // In bridgeless mode, timers are host functions installed from cpp.

Libraries/Utilities/FeatureDetection.js

@@ -0,0 +1,22 @@
+/**
+ * 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
+ * @format
+ */
+
+/**
+ * @return whether or not a @param {function} f is provided natively by calling
+ * `toString` and check if the result includes `[native code]` in it.
+ *
+ * Note that a polyfill can technically fake this behavior but few does it.
+ * Therefore, this is usually good enough for our purpose.
+ */
+function isNativeFunction(f: Function): boolean {
+  return typeof f === 'function' && f.toString().indexOf('[native code]') > -1;
+}
+
+module.exports = {isNativeFunction};