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 7f4f6838c81b86ac8ba0a2454a7f6970164a5456..4580f99b9ae90401975520c9a23bf760bb4212d6 100644
--- a/ash/common/wm_shell.cc
+++ b/ash/common/wm_shell.cc
@@ -151,11 +151,6 @@ 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_)
@@ -272,9 +267,12 @@ WmShell::WmShell(std::unique_ptr<ShellDelegate> shell_delegate)
   keyboard_brightness_control_delegate_.reset(new KeyboardBrightnessController);
   vpn_list_ = base::MakeUnique<VpnList>();
 #endif
+  session_controller_->AddSessionStateObserver(this);
 }
 
-WmShell::~WmShell() {}
+WmShell::~WmShell() {
+  session_controller_->RemoveSessionStateObserver(this);
+}
 
 WmRootWindowController* WmShell::GetPrimaryRootWindowController() {
   return GetPrimaryRootWindow()->GetRootWindowController();
@@ -415,4 +413,14 @@ void WmShell::SetAcceleratorController(
   accelerator_controller_ = std::move(accelerator_controller);
 }
 
+void WmShell::SessionStateChanged(session_manager::SessionState state) {
+  // Create the shelf when the first session becomes active. There's no need to
+  // recreate it when multiprofile sessions are added.
+  if (state != session_manager::SessionState::ACTIVE || first_session_active_)
+    return;
+
+  WmShell::Get()->CreateShelf();

[msw, 2016/12/20 15:37:30]

Isn't WmShell::Get() equivalent to |this|, and not needed?

[James Cook, 2016/12/20 17:27:19]

Whoops, done.

+  first_session_active_ = true;

[msw, 2016/12/20 15:37:30]

Should this ever be reset to false, eg. when the user logs out, or is the
WmShell object destroyed then? Otherwise, it seems like the second user to log
in won't get a shelf, right? You can go back to calling CreateShelf multiple
times if that's safe (with a comment to that effect).

[James Cook, 2016/12/20 17:27:19]

Changed to always attempt to create the shelf (which is safe) and added a
comment. I'm pretty sure that logout restarts the browser, but there's no harm
in calling it twice. This will also make it easier to switch to "PopulateShelf"
in the future when we always create the ShelfView.

+}
+
 }  // namespace ash