[DevTools] Add platform/module.json file to devtools.gypi.

This was missed in r184865.

TBR=apavlov
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/706183002

git-svn-id: svn://svn.chromium.org/blink/trunk@184961 bbb929c8-8fbe-4397-9dbb-9b2b20218538