Revert of DevTools: Load module scripts in parallel in the debug_devtools=1 mode (patchset #1 id:1 of https://codereview.chromium.org/680883002/)

Reason for revert:
This breaks hosted mode (used for remote debugging): the exception is thrown when InspectorBackendCommands.js failed to load.

Original issue's description:
> DevTools: Load module scripts in parallel in the debug_devtools=1 mode
> 
> R=pfeldman
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184531

TBR=pfeldman@chromium.org,apavlov@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/652363004

git-svn-id: svn://svn.chromium.org/blink/trunk@184564 bbb929c8-8fbe-4397-9dbb-9b2b20218538