git cl upload: cc + reviewers in git push for chromium host.

For other hosts, behavior is not changed.

Tested on this very CL:
  To https://chromium.googlesource.com/chromium/tools/depot_tools.git
    * [new branch]        9057c2235b096f1feae61d65569641fc7c08a0e2 ->
      refs/for/refs/heads/master%ready,notify=ALL,m=Initial_upload,r=ehmaldonado,cc=chromium-reviews@chromium.org,cc=iannucci+depot_tools@chromium.org,hashtag=git-cl-upload

R=ehmaldonado

Bug: 877717
Change-Id: I951fc576105211590c6c303ce0ed2fe142628224
Reviewed-on: https://chromium-review.googlesource.com/c/1307051
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
diff --git a/git_cl.py b/git_cl.py
index 3d96e6a..a46509c 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -2872,8 +2872,12 @@
     cc = filter(None, [email.strip() for email in cc])
     if change_desc.get_cced():
       cc.extend(change_desc.get_cced())
-    valid_accounts = gerrit_util.ValidAccounts(
-        self._GetGerritHost(), reviewers + cc)
+    if self._GetGerritHost() == 'chromium-review.googlesource.com':
+      valid_accounts = set(reviewers + cc)
+      # TODO(crbug/877717): relax this for all hosts.
+    else:
+      valid_accounts = gerrit_util.ValidAccounts(
+          self._GetGerritHost(), reviewers + cc)
     logging.info('accounts %s are recognized, %s invalid',
                  sorted(valid_accounts),
                  set(reviewers + cc).difference(set(valid_accounts)))
@@ -2918,7 +2922,6 @@
         refspec_opts.append('cc=%s' % c)
         cc.remove(c)
 
-
     if options.topic:
       # Documentation on Gerrit topics is here:
       # https://gerrit-review.googlesource.com/Documentation/user-upload.html#topic