Fix hostname validating regex for one letter subdomains

Bug: 981200
Change-Id: I910ba2d30e92c6a3605fb3bac98618d0491a5859
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1730903Reviewed-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683615}

chrome/browser/chromeos/policy/device_policy_decoder_chromeos.cc

@@ -43,7 +43,7 @@ namespace em = enterprise_management;
 namespace policy {
 
 // A pattern for validating hostnames.
-const char hostNameRegex[] = "^([A-z0-9][A-z0-9-]+\\.)+[A-z0-9]+$";
+const char hostNameRegex[] = "^([A-z0-9][A-z0-9-]*\\.)+[A-z0-9]+$";
 
 namespace {