Revert "DevTools: Load document (html) content from disk cache in page agent enabling."

BUG=385549
TBR=pfeldman

Review URL: https://codereview.chromium.org/338253007

git-svn-id: svn://svn.chromium.org/blink/trunk@176333 bbb929c8-8fbe-4397-9dbb-9b2b20218538