DevTools: highlight markdown files

This patch adds markdown codemirror mode.

R=dgozman

Change-Id: I276643701e34c0af2edc0fdb18f0c2411b1614fc
Reviewed-on: https://chromium-review.googlesource.com/912010
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536280}
4 files changed