Revert 169354 "DevTools: track stylesheets by document, not loca..."

Caused a crash on linux asan bot, see crbug.com/353257

> DevTools: track stylesheets by document, not local frame.
> 
> R=lushnikov@chromium.org, vsevik@chromium.org
> 
> Review URL: https://codereview.chromium.org/201683002

TBR=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/202443003

git-svn-id: svn://svn.chromium.org/blink/trunk@169389 bbb929c8-8fbe-4397-9dbb-9b2b20218538