Refactor DownloadProtectionService for modularity.

Pull the subclasses within DownloadProtectionService out into their own
files. Also, move common dependencies to download_protection_util.h.

Bug: 721964,689520
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I73fb2479c6a168ad6e3be7c8f76b89e33c05d7ff
Reviewed-on: https://chromium-review.googlesource.com/583999
Commit-Queue: Micah Morton <mortonm@google.com>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Nathan Parker <nparker@chromium.org>
Reviewed-by: Jialiu Lin <jialiul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494982}
57 files changed