Introduce ash mojo interface for lock screen action handlers

ash/BUILD.gn

Index: ash/BUILD.gn
diff --git a/ash/BUILD.gn b/ash/BUILD.gn
index 6f666d18eac9e76224da582bc00a618fc2d1d0ac..4ae4a8fab217757ff324b2646f601de287abe402 100644
--- a/ash/BUILD.gn
+++ b/ash/BUILD.gn
@@ -582,6 +582,9 @@ component("ash") {
     "touch/touch_observer_hud.h",
     "touch/touch_uma.cc",
     "touch/touch_uma.h",
+    "tray_action/tray_action.cc",
+    "tray_action/tray_action.h",
+    "tray_action/tray_action_observer.h",
     "utility/screenshot_controller.cc",
     "utility/screenshot_controller.h",
     "utility/transformer_util.cc",
@@ -1219,6 +1222,7 @@ source_set("common_unittests") {
     "system/web_notification/web_notification_tray_unittest.cc",
     "test/ash_test_helper_unittest.cc",
     "tooltips/tooltip_controller_unittest.cc",
+    "tray_action/tray_action_unittest.cc",
     "wallpaper/wallpaper_controller_unittest.cc",
     "window_user_data_unittest.cc",
     "wm/ash_focus_rules_unittest.cc",