All other DEPS-using projects have migrated away from deps_os, so
let us do the same. This also fixes the roll-svn-dep bug.

Bug: chromium:798336, libyuv:768
Change-Id: I1528720766af9a0f0d4906aa0ad440408232f6d0
Reviewed-on: https://chromium-review.googlesource.com/848812
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Reviewed-by: Frank Barchard <fbarchard@chromium.org>