DevTools: Introduce scripts for generating png images from svg images and presubmit check for them.

This patch adds a script to convert svg images to png images and a script to optimize png images in the devtools front-end Images folder.
Presubmit check also added that checks that these scripts were used for all svg files that were changed/added with a patch.

Landing PRESUBMIT.py changes TBR since I am only deleting devtools checks from this file.

R=eustas@chromium.org, pfeldman@chromium.org, eustas, pfeldman
TBR=thakis

Review URL: https://codereview.chromium.org/130423008

git-svn-id: svn://svn.chromium.org/blink/trunk@165926 bbb929c8-8fbe-4397-9dbb-9b2b20218538