Re-factor system tray code controlling launcher visibility

ash/system/status_area_widget.h

Index: ash/system/status_area_widget.h
diff --git a/ash/system/status_area_widget.h b/ash/system/status_area_widget.h
index 376bbd9dde488bf37bc6de8ce8447ca2e92fa7b6..fede19fc30a0b6b5e127fbd906c1839fffa8f6a0 100644
--- a/ash/system/status_area_widget.h
+++ b/ash/system/status_area_widget.h
@@ -56,6 +56,11 @@ class ASH_EXPORT StatusAreaWidget : public views::Widget {
   // notification tray.
   void UpdateAfterLoginStatusChange(user::LoginStatus login_status);
 
+  // Called whenever the launcher auto-hide behavior may need updating.
+  // This sets should_show_launcher_ and calls
+  // ShelfLayoutManager::UpdateAutoHideState() if the state has changed.
+  void UpdateShouldShowLauncher();
+
   internal::StatusAreaWidgetDelegate* status_area_widget_delegate() {
     return status_area_widget_delegate_;
   }
@@ -69,6 +74,8 @@ class ASH_EXPORT StatusAreaWidget : public views::Widget {
 
   user::LoginStatus login_status() const { return login_status_; }
 
+  bool should_show_launcher() const { return should_show_launcher_; }
+
  private:
   void AddSystemTray(ShellDelegate* shell_delegate);
   void AddWebNotificationTray();
@@ -79,6 +86,7 @@ class ASH_EXPORT StatusAreaWidget : public views::Widget {
   SystemTray* system_tray_;
   WebNotificationTray* web_notification_tray_;
   user::LoginStatus login_status_;
+  bool should_show_launcher_;
 
   DISALLOW_COPY_AND_ASSIGN(StatusAreaWidget);
 };