chromeos: Fix shelf appearing at login screen under mash

ash/mus/bridge/wm_shell_mus.cc

Index: ash/mus/bridge/wm_shell_mus.cc
diff --git a/ash/mus/bridge/wm_shell_mus.cc b/ash/mus/bridge/wm_shell_mus.cc
index d9e9bd2b9f0e427b0be43de396fede0f96d1a467..d5edcc16ea928dbe91e396c54aa802b07923d54c 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -392,6 +392,11 @@ void WmShellMus::OnOverviewModeEnded() {
     observer.OnOverviewModeEnded();
 }
 
+void WmShellMus::OnUserSessionStateActive() {
+  CreateShelf();
+  // Mash has a different codepath for virtual keyboard initialization.

[msw, 2016/12/16 16:26:20]

This comment is a bit odd, since nothing keyboard related is happening here.
Remove the comment or provide some context, like "WmShelAura initializes the
Keyboard at this stage, but Mash does so elsewhere."

[James Cook, 2016/12/20 04:02:43]

This codepath doesn't exist anymore.

+}
+
 SessionStateDelegate* WmShellMus::GetSessionStateDelegate() {
   return session_state_delegate_.get();
 }