Reland "arc: Show placeholder notification for ARCVM /data migration"

This is a reland of commit 00d68a688616f0ee9129762a2be577603030f20d

The original change was reverted due to unit test failures on bots with
Asan/Lsan or Msan enabled. It was because the teardown order of
ArcSessionManager and ArcVmDataMigrationNotifier was wrong.
Now the teardown order is fixed so that it matches the real order, and
we have confirmed that the fix makes the tests pass on Asan/Lsan and
Msan enabled bots.

Original change's description:
> arc: Show placeholder notification for ARCVM /data migration
>
> If ARCVM /data migration is enabled, a notification to inform the user
> of an available update (= the migration) is shown when an ARC session is
> started.
>
> If the user clicks the Update button, another confirmation dialog will
> be shown to ask the user to confirm the migration, which will be
> implemented in another CL.
>
> Icons and strings are tentative placeholders and will be replaced once
> the final design decision is made.
>
> Bug: b:258278176
> Test: --enable-features=ArcVmDataMigration
> Test: unit_tests --gtest_filter="ArcVmDataMigrationNotifierTest.*"
>
> Change-Id: I8535ed02b59d282239ae9bc057fdce80786ce3fd
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4023144
> Reviewed-by: Satoshi Niwa <niwa@chromium.org>
> Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
> Reviewed-by: Alex Newcomer <newcomer@chromium.org>
> Commit-Queue: Youkichi Hosoi <youkichihosoi@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1077049}

Bug: b:258278176
Change-Id: Ib83bc5e82eca691a76974dc03a240b2612910be9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4065060
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Youkichi Hosoi <youkichihosoi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1077706}