[subresource_filter] add //chrome level unit test harness

The subresource_filter code is getting more dependent on //chrome level
things like content settings. Right now it is tricky to get end to end
testing without bringing up the whole browser, even for very simple
tests.

This patch adds a test harness which sets up all the necessary
dependencies for subresource filtering. This should make testing new
features easy and fast.

BUG=709768

Review-Url: https://codereview.chromium.org/2820933002
Cr-Commit-Position: refs/heads/master@{#466270}
9 files changed