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

ash/common/wm_shell.cc

Index: ash/common/wm_shell.cc
diff --git a/ash/common/wm_shell.cc b/ash/common/wm_shell.cc
index 40155129d13f97576d0bec8745c7ba4119b13ea4..690780d9c621b30e78606fab9a79d8c76cd6f11d 100644
--- a/ash/common/wm_shell.cc
+++ b/ash/common/wm_shell.cc
@@ -153,11 +153,6 @@ void WmShell::CreateShelf() {
     root_window->GetRootWindowController()->CreateShelf();
 }
 
-void WmShell::ShowShelf() {
-  for (WmWindow* root_window : GetAllRootWindows())
-    root_window->GetRootWindowController()->ShowShelf();
-}
-
 void WmShell::CreateShelfDelegate() {
   // May be called multiple times as shelves are created and destroyed.
   if (shelf_delegate_)
@@ -274,6 +269,7 @@ WmShell::WmShell(std::unique_ptr<ShellDelegate> shell_delegate)
       window_cycle_controller_(base::MakeUnique<WindowCycleController>()),
       window_selector_controller_(
           base::MakeUnique<WindowSelectorController>()) {
+  session_controller_->AddSessionStateObserver(this);
 
   prefs::mojom::PreferencesManagerPtr pref_manager_ptr;
   // Can be null in tests.
@@ -284,7 +280,9 @@ WmShell::WmShell(std::unique_ptr<ShellDelegate> shell_delegate)
   pref_store_ = new preferences::PrefObserverStore(std::move(pref_manager_ptr));
 }
 
-WmShell::~WmShell() {}
+WmShell::~WmShell() {
+  session_controller_->RemoveSessionStateObserver(this);
+}
 
 RootWindowController* WmShell::GetPrimaryRootWindowController() {
   return GetPrimaryRootWindow()->GetRootWindowController();
@@ -418,4 +416,11 @@ void WmShell::SetAcceleratorController(
   accelerator_controller_ = std::move(accelerator_controller);
 }
 
+void WmShell::SessionStateChanged(session_manager::SessionState state) {
+  // Create the shelf when a session becomes active. It's safe to do this
+  // multiple times (e.g. initial login vs. multiprofile add session).
+  if (state == session_manager::SessionState::ACTIVE)
+    CreateShelf();
+}
+
 }  // namespace ash