[piexwasm] Require onPiexModuleFailed via Closure markup

Require onPiexModuleFailed argument to PiexLoader.load: update Closure
markup to say that: clients do need to handle WASM module failure.

Bug: 1145029
Change-Id: If1819ff780433772d0aa135687a4f2af1741103a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2557765Reviewed-by: Alex Danilo <adanilo@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830857}

ui/file_manager/image_loader/piex_loader.js

@@ -631,7 +631,7 @@ const PiexLoader = {};
  * the caller should initiate failure recovery steps.
  *
  * @param {!ArrayBuffer|!File|string} source
- * @param {function()} onPiexModuleFailed
+ * @param {!function()} onPiexModuleFailed
  * @return {!Promise<!PiexLoaderResponse>}
  */
 PiexLoader.load = function(source, onPiexModuleFailed) {