Rename wholeSubtree to adjacent.

Using subtree invalidation is a current consequence of adjacent
combinators. Using "adjacent" as a feature should be more understandable.

Also tried to make the code more readable for the combinator handling in
general.

R=chrishtr@chromium.org,esprehn@chromium.org

Review URL: https://codereview.chromium.org/641583002

git-svn-id: svn://svn.chromium.org/blink/trunk@183571 bbb929c8-8fbe-4397-9dbb-9b2b20218538