Stop the OverviewButton from appearing on the Add-User screen

ash/system/overview/overview_button_tray.cc

Index: ash/system/overview/overview_button_tray.cc
diff --git a/ash/system/overview/overview_button_tray.cc b/ash/system/overview/overview_button_tray.cc
index edd5d67dd0697dd2598133cc5289d83e7511831f..f5295b52fd04bddb003cc8c118ee915b54c82f71 100644
--- a/ash/system/overview/overview_button_tray.cc
+++ b/ash/system/overview/overview_button_tray.cc
@@ -4,6 +4,7 @@
 
 #include "ash/system/overview/overview_button_tray.h"
 
+#include "ash/session/session_state_delegate.h"
 #include "ash/shelf/shelf_types.h"
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray_delegate.h"
@@ -42,10 +43,13 @@ OverviewButtonTray::OverviewButtonTray(StatusAreaWidget* status_area_widget)
   tray_container()->AddChildView(icon_);
 
   Shell::GetInstance()->AddShellObserver(this);
+  Shell::GetInstance()->session_state_delegate()->AddSessionStateObserver(this);
 }
 
 OverviewButtonTray::~OverviewButtonTray() {
   Shell::GetInstance()->RemoveShellObserver(this);
+  Shell::GetInstance()->session_state_delegate()->RemoveSessionStateObserver(
+      this);
 }
 
 void OverviewButtonTray::UpdateAfterLoginStatusChange(
@@ -62,6 +66,11 @@ bool OverviewButtonTray::PerformAction(const ui::Event& event) {
   return true;
 }
 
+void OverviewButtonTray::SessionStateChanged(
+    SessionStateDelegate::SessionState state) {
+  UpdateIconVisibility();
+}
+
 void OverviewButtonTray::OnMaximizeModeStarted() {
   UpdateIconVisibility();
 }
@@ -115,9 +124,22 @@ void OverviewButtonTray::SetIconBorderForShelfAlignment() {
 }
 
 void OverviewButtonTray::UpdateIconVisibility() {
-  SetVisible(Shell::GetInstance()->maximize_mode_controller()->
-                 IsMaximizeModeWindowManagerEnabled() &&
-             Shell::GetInstance()->window_selector_controller()->CanSelect());
+  // The visibility of the OverviewButtonTray has diverge from
+  // WindowSelectorController::CanSelect. The visibility of the button should
+  // not change during transient times in which CanSelect is false. Such as when
+  // a modal dialog is present.
+  Shell* shell = Shell::GetInstance();
+  SessionStateDelegate* session_state_delegate =
+      shell->session_state_delegate();
+
+  SetVisible(
+      shell->maximize_mode_controller()->IsMaximizeModeWindowManagerEnabled() &&
+      session_state_delegate->IsActiveUserSessionStarted() &&
+      !session_state_delegate->IsScreenLocked() &&
+      session_state_delegate->GetSessionState() ==
+          SessionStateDelegate::SESSION_STATE_ACTIVE &&

[sadrul, 2015/06/03 19:08:36]

This ... is a bit complex. Can this be made better? e.g. have a separate state
for locked screen, so that just checking SESSION_STATE_ACTIVE here is
sufficient? and/or, update IsActiveUserSessionStarted() so that it does the
checking for screen-lock and session-state? At this current state, this API
seems fairly unusable for someone not already closely familiar with it.

[jonross, 2015/06/04 17:38:22]

The "Active Session" term has become a bit overloaded.

Right now:
  - IsActiveUserSessionStarted tracks if a user login status, can precede
completion of UI creation. Some usage current expects it to be separated from UI
  - GetSessionState is a login UI flow state
  - IsScreenLocked is currently separated from GetSessionState

I really think that this state tracking should be merged in the
SessionStateDelegate. Then code using them to be updated.

The fact that the type of user is tracked through the SystemTrayDelegate is also
a bit confusing.

[jonross, 2015/06/04 17:55:54]

Filed crbug.com/496761 to cover a refactor of SessionStateDelegate

+      shell->system_tray_delegate()->GetUserLoginStatus() !=
+          user::LOGGED_IN_KIOSK_APP);
 }
 
 }  // namespace ash