Accept URLs in 'git cl issue'

There's no reason not to, since it is pretty easy, and other
commands like "git cl patch" already do so.

Bug: 733715
Change-Id: I3396153ef11bfdbbf09b8a7f54f9a5b1047e290f
Reviewed-on: https://chromium-review.googlesource.com/537113Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

git_cl.py

@@ -4428,7 +4428,6 @@ def CMDissue(parser, args):
   if options.reverse:
     branches = RunGit(['for-each-ref', 'refs/heads',
                        '--format=%(refname:short)']).splitlines()
-
     # Reverse issue lookup.
     issue_branch_map = {}
     for branch in branches:
@@ -4445,15 +4444,18 @@ def CMDissue(parser, args):
           issue, ', '.join(issue_branch_map.get(int(issue)) or ('None',))))
     if options.json:
       write_json(options.json, result)
-  else:
-    cl = Changelist(codereview=options.forced_codereview)
+    return 0
+
   if len(args) > 0:
-      try:
-        issue = int(args[0])
-      except ValueError:
-        DieWithError('Pass a number to set the issue or none to list it.\n'
+    issue = ParseIssueNumberArgument(args[0], options.forced_codereview)
+    if not issue.valid:
+      DieWithError('Pass a url or number to set the issue, 0 to unset it, '
+                   'or no argument to list it.\n'
                    'Maybe you want to run git cl status?')
-      cl.SetIssue(issue)
+    cl = Changelist(codereview=issue.codereview)
+    cl.SetIssue(issue.issue)
+  else:
+    cl = Changelist(codereview=options.forced_codereview)
   print('Issue number: %s (%s)' % (cl.GetIssue(), cl.GetIssueURL()))
   if options.json:
     write_json(options.json, {