Direct adjacent rules should not recalcStyle on all siblings

When I merged the whitespace loop into Element::recalcStyle I refactored the
loop but got the order of some of the operations wrong and now we check for
childRulesChanged after doing setNeedsStyleRecalc() which meant that
forceCheckOfNextElementSibling became "force check of all following elements".

While this made us more correct since things like :hover + foo + bar started
working (contrary to the comment above the loop), it means we recalc style
many more elements than we would have before.

This patch moves the line back to the correct location to avoid doing so much
extra recalc.

Review URL: https://chromiumcodereview.appspot.com/23035003

git-svn-id: svn://svn.chromium.org/blink/trunk@156058 bbb929c8-8fbe-4397-9dbb-9b2b20218538