[subresource_filter] Add metrics for UI / related things

This patch adds a new profile keyed service for keeping profile-scoped
state for the subresource filter.

For now, this is used to implement a content_service::Observer to be
notified of any ContentSettings changes for that particular profile.

BUG=705260

Review-Url: https://codereview.chromium.org/2777093007
Cr-Commit-Position: refs/heads/master@{#460792}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 771af088..9c61162e 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1277,6 +1277,8 @@
     "subresource_filter/chrome_subresource_filter_client.h",
     "subresource_filter/navigation_throttle_util.cc",
     "subresource_filter/navigation_throttle_util.h",
+    "subresource_filter/subresource_filter_content_settings_observer_factory.cc",
+    "subresource_filter/subresource_filter_content_settings_observer_factory.h",
     "sync/chrome_sync_client.cc",
     "sync/chrome_sync_client.h",
     "sync/glue/extensions_activity_monitor.cc",