Implement a dummy onGetActionsRequested listener.

The FSP implementation doesn't handle the difference between "not
implemented" and "error". Zip archiver doesn't provide any custom
actions, but FSP interprets this as an error and that bubbles back to
the Files App.

BUG=679634

Change-Id: I5b52c64b0d01bd700ea4509d046630396afa756c
Reviewed-on: https://chromium-review.googlesource.com/c/1341435Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Anand Mistry <amistry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609171}

chrome/browser/resources/chromeos/zip_archiver/js/background.js

@@ -30,6 +30,12 @@ function setupZipArchiver() {
   chrome.fileSystemProvider.onReadFileRequested.addListener(
       unpacker.app.onReadFileRequested);
 
+  // Provide a dummy onGetActionsRequested implementation to make FSP happy.
+  chrome.fileSystemProvider.onGetActionsRequested.addListener(
+      (options, success, error) => {
+        success([]);
+      });
+
   // Clean all temporary files inside the work directory, just in case the
   // extension aborted previously without removing ones.
   unpacker.app.cleanWorkDirectory();