Add chromium/_bad_scm to .gitignore

When Chromium decides to move conflicting dependencies
to the _bad_scm directory it is possible to end up with
problems when that directory gets added to the local index.
Ignoring it should avoid such problems.

R=hbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45969004

Cr-Commit-Position: refs/heads/master@{#8988}
1 file changed