Split SnapshotController into online and offline versions.

To make the Resource Percentage work easier, we are splitting the
snapshot controller into a foreground and a background version.

Bug: 699313
Change-Id: Ideeea7d644a903290d9eeae2d7ab700ab0ff50b6
Reviewed-on: https://chromium-review.googlesource.com/1136023
Reviewed-by: Dmitry Titov <dimich@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Commit-Queue: Peter Williamson <petewil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578351}
12 files changed