ash: Report internal errors when fetching calendar events

CalendarEventFetch now also requires a callback for handling
"internal" errors, i.e. any errors that didn't come from the Calendar
API.  As with the FetchCompleteCallback we supply, CalendarModel's
FetchInternalErrorCallback destroys the CalendarEventFetch object that
invoked it.

Add a timer for each calendar event fetch, to fire if we go too long
without receiving a response from the Calendar API.  In this case we
report an internal error of TIMEOUT.

Bug: 1298187
Change-Id: I94e5a0a48f787bf00279068fd4a8f14cc95db460
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3472463
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Jiaming Cheng <jiamingc@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Roger Tinkoff <rtinkoff@google.com>
Cr-Commit-Position: refs/heads/main@{#972768}