FilesApp crostini shared folder: show toast on startup

The first time when FilesApp is started in a session, it should
show a toast displaying the number of folders currently
shared with crostini, and a link to manage sharing.

* Added state to crostini::CrostiniSharePath keyed profile service
for whether the GetPersistedSharedPaths function has been called
in a session.

* Change FileManagerPrivateInternalGetCrostiniSharedPathsFunction
to call file_manager::util::ExtractMountNameAndFullPath which allows
Entry to be set sync rather than async via
file_manager::util::ConvertFileDefinitionListToEntryDefinitionList

* Changed CommandHandler.recordMenuItemSelected to be public to
allow us to record UMA when user selects 'Manage sharing' in the
startup toast.

Bug: 878324
Change-Id: I283eb49b61bafdde414a7d1b7aa0723997687742
Reviewed-on: https://chromium-review.googlesource.com/c/1350375
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610999}
16 files changed