Re-reland: chromeos: Fix shelf appearing at login screen under mash

chrome/browser/ui/ash/session_controller_client.cc

Index: chrome/browser/ui/ash/session_controller_client.cc
diff --git a/chrome/browser/ui/ash/session_controller_client.cc b/chrome/browser/ui/ash/session_controller_client.cc
index b171cf2fb7707f3345cb3223abd6af7582f7aaee..fad60d44bd2d2948fd93239636db007fd33bbb8a 100644
--- a/chrome/browser/ui/ash/session_controller_client.cc
+++ b/chrome/browser/ui/ash/session_controller_client.cc
@@ -34,6 +34,8 @@ using user_manager::UserList;
 
 namespace {
 
+SessionControllerClient* g_instance = nullptr;
+
 uint32_t GetSessionId(const User* user) {
   const UserList logged_in_users = UserManager::Get()->GetLoggedInUsers();
   // TODO(xiyuan): Update with real session id when user session tracking
@@ -83,9 +85,15 @@ SessionControllerClient::SessionControllerClient() : binding_(this) {
   SendSessionInfoIfChanged();
   // User sessions and their order will be sent via UserSessionStateObserver
   // even for crash-n-restart.
+
+  DCHECK(!g_instance);
+  g_instance = this;
 }
 
 SessionControllerClient::~SessionControllerClient() {
+  DCHECK_EQ(this, g_instance);
+  g_instance = nullptr;
+
   SessionManager::Get()->RemoveObserver(this);
   UserManager::Get()->RemoveSessionStateObserver(this);
 }
@@ -225,6 +233,11 @@ void SessionControllerClient::DoCycleActiveUser(bool next_user) {
   DoSwitchActiveUser(account_id);
 }
 
+// static
+void SessionControllerClient::FlushForTesting() {
+  g_instance->session_controller_.FlushForTesting();
+}
+
 void SessionControllerClient::OnSessionStateChanged() {
   SendSessionInfoIfChanged();
 }