[Read Aloud] Generic download error message

Show "download failed" whenever there is an unspecified
error downloading a voice pack.

https://screenshot.googleplex.com/7X9dQYidJrReTtV.png

Fixed: 345752584
Change-Id: I6a198ac63bca322f44d7ca1b1549b1c9c5815199
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5609026


Reviewed-by: Jocelyn Tran <jocelyntran@google.com>
Commit-Queue: Lauren Winston <lwinston@google.com>
Reviewed-by: Eitan Goldberger <eitang@google.com>
Cr-Commit-Position: refs/heads/main@{#1312815}