DevTools: Fix generation of devtools_resources.grd in debug_devtools mode

All resources were put into the bundle root rather than into their respective folders

TBR=pfeldman

Review URL: https://codereview.chromium.org/273673002

git-svn-id: svn://svn.chromium.org/blink/trunk@173524 bbb929c8-8fbe-4397-9dbb-9b2b20218538