emacs: cros_sdk tramp integration.

With this, opening files starting with `/cros::` enters cros_sdk chroot.

BUG=None
TEST=(load-file "~/src/cros-work2/src/platform/dev/contrib/emacs/cros-sdk-tramp.el")
  and open /cros::

Change-Id: Iff3962e3793720bb5fe4868e69c19de7faf529af
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2936169
Commit-Queue: Junichi Uekawa <uekawa@chromium.org>
Tested-by: Junichi Uekawa <uekawa@chromium.org>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
2 files changed