Revert r174557 "DevTools: Load document (html) content from disk cache in page agent enabling."

Backend stops responding in certain cases.

TBR=vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/294053010

git-svn-id: svn://svn.chromium.org/blink/trunk@174578 bbb929c8-8fbe-4397-9dbb-9b2b20218538