GitLab

Modified export/import handling from CrostiniManager to
take a CrostiniResultMessageCallback which receives both
a CrostiniResult and a base::string16 error message which
can be displayed in the notification.

Strings from https://docs.google.com/spreadsheets/d/1paVaVV2azeuAHnxHT4jQ402VvaZ7Z8btZ5e_y7rPRnE/edit#gid=0

Bug: 933948
Change-Id: I2451492d85cd8263a8914a31b82162d4e93a77de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1558559
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649780}