attach should correctly update the style bits so recalcStyle doesn't have to

Node::attach already clears needsStyleRecalc which means the code in recalcStyle
to do it was not needed. By making ContainerNode::attach clear the
childNeedsRecalcStyle bit we can remove that code from recalc style as well.

Review URL: https://chromiumcodereview.appspot.com/22640005

git-svn-id: svn://svn.chromium.org/blink/trunk@155826 bbb929c8-8fbe-4397-9dbb-9b2b20218538