Add rules to the rule set according to likelihood of being infrequent, regardless of the order
of rules across SubSelector relations in the selector.

Add a test framework for CSS rule tests, and a unit test for RuleSet.

BUG=338037

Review URL: https://codereview.chromium.org/130423015

git-svn-id: svn://svn.chromium.org/blink/trunk@166324 bbb929c8-8fbe-4397-9dbb-9b2b20218538