Store/restore persistent USB permissions.

Stores and restores persistent USB permission with Chrome prefs.

Bug: 776476
Bug: b:24572867
Change-Id: I008166a32d47cba2edbdc54858b807491add6858
Reviewed-on: https://chromium-review.googlesource.com/944249
Commit-Queue: Long Cheng <lgcheng@google.com>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541679}
6 files changed