Reason for revert: This is breaking official release scripts, which have long
used "None" URL functionality to allow gclient commands to run against
"local" DEPS (buildspec) files. Please do not remove this behavior.

This reverts the following commits:
  ebdd0db4: "gclient: Remove URLs from hierarchy."
  54a5c2ba: "gclient: Refactor PrintRevInfo"
  083eb25f: "gclient: Don't allow URL to be None."

BUG=846194

TBR=agable@chromium.org,ehmaldonado@chromium.org

Change-Id: Ibdd5581889bd4afd86474199c7b64555f01bbbca
Reviewed-on: https://chromium-review.googlesource.com/1070893
Commit-Queue: Michael Moss <mmoss@chromium.org>
Reviewed-by: Michael Moss <mmoss@chromium.org>