Split Element::recalcStyle into recalcOwnStyle and recalcChildStyle

recalcStyle has become too big, by moving around the local variables based on the
scope where they're needed we can move most of the function out into recalcOwnStyle
where your own style is updated and recalcChildStyle where the style of your
children is calculated.

I also renamed the Detach StyleChange value to be Reattach since that's what it
really means.

There should be no behavior change, I just refactored the code.

Review URL: https://chromiumcodereview.appspot.com/23592004

git-svn-id: svn://svn.chromium.org/blink/trunk@156820 bbb929c8-8fbe-4397-9dbb-9b2b20218538