Grant permissions to other profile files on demand.
Previously, Files app was being granted permissions to all volumes even if
not all of them were requested or needed.
This is the first patch of the larger effort in order to grant permissions to
only what's needed. This CL grants pemissions to other-profile files before
performing a paste operation for that files.
TEST=Tested manually with multiple profiles.
BUG=323422
R=fukino@chromium.org, hirono@chromium.org, isherman@chromium.org, kinaba@chromium.org
Review URL: https://codereview.chromium.org/
993873002
Cr-Commit-Position: refs/heads/master@{#320063}