Revert 169371 "DevTools: defer styles delta calculation to until..."

This is in order to revert 169354, which caused a crash on ASAN bot.

See crbug.com/353257

> DevTools: defer styles delta calculation to until the end of the task.
> 
> BUG=289708
> R=vsevik@chromium.org
> 
> Review URL: https://codereview.chromium.org/201363002

TBR=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/196743008

git-svn-id: svn://svn.chromium.org/blink/trunk@169388 bbb929c8-8fbe-4397-9dbb-9b2b20218538