Send manager to gaia login screen via the 'devicemanager' query param.

Manager may be either a domain (foo.com) or the email address of the
admin of the organization (user@foo.com).

BUG=chromium:1081272,b:169152988

Change-Id: I11be31e4ea04bc637c700b6ebedbe94b67cd223b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2467981
Commit-Queue: Brian Malcolm <bmalcolm@chromium.org>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816796}

chrome/browser/resources/gaia_auth_host/authenticator.js

@@ -640,6 +640,9 @@ cr.define('cr.login', function() {
       if (data.enterpriseDisplayDomain) {
         url = appendParam(url, 'manageddomain', data.enterpriseDisplayDomain);
       }
+      if (data.enterpriseDomainManager) {
+        url = appendParam(url, 'devicemanager', data.enterpriseDomainManager);
+      }
       if (data.clientVersion) {
         url = appendParam(url, 'client_version', data.clientVersion);
       }