fixup! vfs: forward the watchFile listener through RealFSProvider

Author: trivikr

test/parallel/test-vfs-real-provider-watch.js

@@ -41,8 +41,12 @@ assert.strictEqual(myVfs.provider.supportsWatch, true);
   fs.writeFileSync(path.join(root, 'wf.txt'), 'a');
   const listener = common.mustCall();
   myVfs.watchFile('/wf.txt', { interval: 10, persistent: false }, listener);
-  fs.writeFileSync(path.join(root, 'wf.txt'), 'b');
+  // libuv's fs_poll records the first stat asynchronously as the baseline and
+  // only reports subsequent changes, so mutate the file only after that
+  // baseline reflects 'a'; otherwise the change is folded into the baseline
+  // and the listener never fires.
+  setTimeout(() => fs.writeFileSync(path.join(root, 'wf.txt'), 'b'), 100);
   setTimeout(() => {
     myVfs.unwatchFile('/wf.txt', listener);
-  }, 50);
+  }, 500);
 }