ChromeOS user_manager: move all KnownUser code to separate file.

chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.cc

Index: chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.cc
diff --git a/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.cc b/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.cc
index d4fb577a85903ce17c5f7927d60a0926e54d3e35..8f2e84d2dca9f8e7111f665582940ba65d8d6a05 100644
--- a/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.cc
+++ b/chrome/browser/chromeos/login/easy_unlock/bootstrap_manager.cc
@@ -9,6 +9,7 @@
 #include "base/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chromeos/login/users/chrome_user_manager_impl.h"
+#include "components/user_manager/known_user.h"
 
 namespace chromeos {
 
@@ -62,7 +63,7 @@ void BootstrapManager::RemoveAllPendingBootstrap() {
     std::string current_user_email;
     if (users->GetString(i, &current_user_email)) {
       delegate_->RemovePendingBootstrapUser(
-          user_manager::UserManager::Get()->GetKnownUserAccountId(
+          user_manager::known_user::GetKnownUserAccountId(
               current_user_email, std::string() /* gaia_id */));
     }
   }