Restore attribute array length in RecursionCheckPoint.

Missing restore caused unnecessary invalidations in subsequent subtrees.

Also renamed a misnamed parameter in RuleFeature.h

R=esprehn
BUG=356196

Review URL: https://codereview.chromium.org/211333003

git-svn-id: svn://svn.chromium.org/blink/trunk@169958 bbb929c8-8fbe-4397-9dbb-9b2b20218538