Don't scope check in SelectorChecker.

Don't scope check in SelectorChecker.

Instead of checking if the rule is from the right scope
in SelectorChecker, just store :host rules separately
and always assume rules are in the right scope in the
checker.

This removes a lot of complexity that was passing around
the scope and checking it, and also the need to plumb
if we're matching UA rules down into the checker.

R=ojan@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/c8184b7e0af33ff4b8c0113aeda23e1e3b6fdf52

[ojan, 2015-01-10 02:58:53]

lgtm

[esprehn, 2015-01-10 03:00:56]

Committed patchset #1 (id:1) manually as
c8184b7e0af33ff4b8c0113aeda23e1e3b6fdf52 (presubmit successful).