Introduce ash mojo interface for lock screen action handlers

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 0a5fb1535017445c8b0bfde0789d97c1c1707e22..dd6595d20838d6fdd6df44b3f4502a124c986ec8 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -157,6 +157,7 @@ class SystemTrayDelegate;
 class SystemTrayNotifier;
 class ToplevelWindowEventHandler;
 class ToastManager;
+class TrayAction;
 class TrayBluetoothHelper;
 class VirtualKeyboardController;
 class VideoActivityNotifier;
@@ -343,6 +344,7 @@ class ASH_EXPORT Shell : public SessionObserver,
   views::corewm::TooltipController* tooltip_controller() {
     return tooltip_controller_.get();
   }
+  TrayAction* tray_action() { return tray_action_.get(); }
   VpnList* vpn_list() { return vpn_list_.get(); }
   WindowCycleController* window_cycle_controller() {
     return window_cycle_controller_.get();
@@ -690,6 +692,7 @@ class ASH_EXPORT Shell : public SessionObserver,
   std::unique_ptr<SystemTrayDelegate> system_tray_delegate_;
   std::unique_ptr<SystemTrayNotifier> system_tray_notifier_;
   std::unique_ptr<ToastManager> toast_manager_;
+  std::unique_ptr<TrayAction> tray_action_;
   std::unique_ptr<VpnList> vpn_list_;
   std::unique_ptr<WallpaperController> wallpaper_controller_;
   std::unique_ptr<WallpaperDelegate> wallpaper_delegate_;