This value is passed in the JSON body, not in the URL, so does not need
to be escaped, otherwise trying to make a branch/tag from another
branch/tag leads to errors like:

  gerrit_util.GerritError: (400) Bad Request: invalid revision "refs%2Fheads%2Fchromium%2F4665"

BUG=1052179
R=linxinan@chromium.org, sokcevic@google.com

Change-Id: I80d709370165fcb84a3375e18b67d4a921be9a8d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3243724
Auto-Submit: Michael Moss <mmoss@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Xinan Lin <linxinan@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>