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This CL depends on issue http://crrev.com/c/1763553 to have a
preference prefs::kArcVisibleExternalStorages. (will rebase later)

prefs::kArcVisibleExternalStorages remembers a list of visible
external storage's UUIDs. "Visible" means that the storage is
visible to Android apps. (i.e. Android apps can use the external
storage to read/write files.)

With this CL, Chrome checks visibility of newly mounted storages
by reading the preference, and tell the visibility to ARC container
using extended MountPointInfo.
In addition, when the remembered UUID list changes, all
external mount points will be remounted in ARC container to
make sure the latest visibility is applied.

Bug: 954228
Change-Id: Ief8bd50881462f7e5ae0677883ac119eacf33f63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1765099
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690798}