Revert of [DevTools] Extract platform module. (patchset #4 id:40002 of https://codereview.chromium.org/673163004/)

Reason for revert:
This breaks DevTools at least in a hosted mode: the front-end does not load, exceptions are thrown from Runtime.js

Original issue's description:
> [DevTools] Extract platform module.
> 
> BUG=none
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184753

TBR=apavlov@chromium.org,pfeldman@chromium.org,vsevik@chromium.org,dgozman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=none

Review URL: https://codereview.chromium.org/692343002

git-svn-id: svn://svn.chromium.org/blink/trunk@184772 bbb929c8-8fbe-4397-9dbb-9b2b20218538