s/styleResolver/ensureStyleResolver and s/resolver/ensureResolver.

This is keeping with our naming convention to indicate that this
a) never returns null
b) does a lot of work

-got rid of one case where we were null checking: hasSelectorForAttribute.
-cleaned up a little code in Document::recalcStyle to only call
ensureStyleResolver once.

The rest is just a straight find and replace.

Review URL: https://codereview.chromium.org/102423003

git-svn-id: svn://svn.chromium.org/blink/trunk@163111 bbb929c8-8fbe-4397-9dbb-9b2b20218538