[Files app] VolumeManagerImpl.initialize() returns a Promise<void>

Change-Id: I739a6ed2a754a17f3899e3b5716f0d0497cb2470
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621790
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: François Degros <fdegros@chromium.org>
Auto-Submit: François Degros <fdegros@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661978}
2 files changed