Replace scheduleForcedStyleRecalc with setNeedsStyleRecalc

Document::scheduleForcedStyleRecalc used a separate bool to track if the
next style recalc should Force, instead we should just use the same model
as Elements where a SubtreeStyleChange means to Force recalc all descendants.

The only quirk here is that SVG's <use> element can go through
DocumentStyleSheetCollection::updateActiveStyleSheets and call into
Document::setNeedsStyleRecalc in the middle of a style recalc so we need
a hack in Document::recalcStyle to notice if the style resolver needs an update
and reschedule it.

I also removed the unused Document::childNeedsAndNotInStyleRecalc() method.

R=eseidel@chromium.org,ojan@chromium.org,

Review URL: https://chromiumcodereview.appspot.com/19144002

git-svn-id: svn://svn.chromium.org/blink/trunk@154719 bbb929c8-8fbe-4397-9dbb-9b2b20218538