Introduce a getdep command to get revision/version/variable value information
as a counterpart for gclient setdep.
It will be useful for autorollers.
Bug: 760633
Change-Id: Iabeae0e78c6fbdcb1a3a79cfb380ac2d83f256d5
Reviewed-on: https://chromium-review.googlesource.com/999171
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>