Add /var/run bind mount for debugfs GPU memory dir
Add /var/run bind mount for debugfs GPU memory dir

/sys/kernel/debug is now only readable by debugd. However, Chrome
sometimes needs real-time access to GEM object memory information in
/sys/kernel/debug/dri/0. Add a bind mount for this specific directory
to /var/run.

BUG=chromium:175828
TEST=manual, verify /var/run/debugfs_gpu exists and files inside are
readable by chronos

Change-Id: I6d7ece58359a2e4a40204ccc94fbe6891df659bc
Reviewed-on: https://gerrit.chromium.org/gerrit/43446
Reviewed-by: Kees Cook <50cb10d2be062154b17ab4d66a4eab34f1cf1c84@chromium.org>
Reviewed-by: Daniel Erat <69d56254d3d393520d06e9838c23c147a5fee7d9@chromium.org>
Commit-Queue: James Cook <3741fd56a17d4d5fef7af0902a2401859b0cd435@chromium.org>
Tested-by: James Cook <3741fd56a17d4d5fef7af0902a2401859b0cd435@chromium.org>

chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager