Use the primary user email as the username on Chrome OS

This is a more accurate representation of who the user is than just
the non-domain part of the email.

Bug: chromium:1859676
Test: manual
Change-Id: I7c63294a925c47184baa28b03be24af975700460
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1865600
Commit-Queue: Yves Arrouye <drcrash@chromium.org>
Commit-Queue: Sergey Poromov <poromov@chromium.org>
Auto-Submit: Yves Arrouye <drcrash@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706994}

components/policy/core/common/cloud/cloud_policy_util.cc

@@ -164,7 +164,7 @@ std::string GetOSUsername() {
   auto* user = user_manager::UserManager::Get()->GetPrimaryUser();
   if (!user)
     return std::string();
-  return user->GetAccountName(/*use_display_email=*/false);
+  return user->GetAccountId().GetUserEmail();
 #else
   NOTREACHED();
   return std::string();