[Kiosk] Record when we receive webstore kiosk app data request failure

Currently, there are a few kiosk tests which are failing when we most
probably get to STATUS_ERROR of KioskAppData. Let's add a log line
which will indicate whether it's a fake cws issue.

Bug: 1044417
Change-Id: I685d10c7cab773d3b7ee5a9f2d426ef2eea8da59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062444Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Anatoliy Potapchuk <apotapchuk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742680}

chrome/browser/chromeos/app_mode/kiosk_app_data.cc

@@ -475,6 +475,7 @@ void KioskAppData::StartFetch() {
 }
 
 void KioskAppData::OnWebstoreRequestFailure(const std::string& extension_id) {
+  LOG(WARNING) << "Webstore request failure for app_id=" << extension_id;
   SetStatus(STATUS_ERROR);
 }