This patch does a few things:
1. Beef up the TestSafeBrowsingDatabaseHelper, so callers can optionally,
   pass in a custom TestV4GetHashProtocolManagerFactory. If this is null,
   then the helper will not mock the v4 hash protocol manager. This
   causes real API requests to go out to the network.

2. Make TestV4Store::MarkPrefixAsBad support multiple prefixes per
   prefix size.

3. Minor cleanups of names and std::make_unique

4. Add a new browser test suite for subresource_filter which uses
   the v4 embedded_test_server request handler, combined with the new
   TestSafeBrowsingDatabaseHelper, to mock out v4 API responses for
   the subresource filter list. This tests enforcement and warning
   variants.

Bug: 775530,737201
Change-Id: Id26b676194fd33c28737bcb693e47ca75145f82f
Reviewed-on: https://chromium-review.googlesource.com/730405


Reviewed-by: Shivani Sharma <shivanisha@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512567}