Download Home : Added feature flag

Added a feature flag "DownloadHomeV2" to enable or disable the new download home.

Bug: 850603
Change-Id: I3e429ab5a6e2afd0ddc36e6052b0ee2baae349d4
Reviewed-on: https://chromium-review.googlesource.com/1137841
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575625}
9 files changed