Add OnDisplayMetricsChanged in DisplayObserver.

ash/display/resolution_notification_controller.cc

Index: ash/display/resolution_notification_controller.cc
diff --git a/ash/display/resolution_notification_controller.cc b/ash/display/resolution_notification_controller.cc
index 2c454029e79d7ef4332407487358a78d00a4289e..315dd5ab5b65cb512ba195cf4f9c1d231443ac29 100644
--- a/ash/display/resolution_notification_controller.cc
+++ b/ash/display/resolution_notification_controller.cc
@@ -285,10 +285,6 @@ void ResolutionNotificationController::RevertResolutionChange() {
       display_id, old_resolution);
 }
 
-void ResolutionNotificationController::OnDisplayBoundsChanged(
-    const gfx::Display& display) {
-}
-
 void ResolutionNotificationController::OnDisplayAdded(
     const gfx::Display& new_display) {
 }
@@ -299,6 +295,10 @@ void ResolutionNotificationController::OnDisplayRemoved(
     RevertResolutionChange();
 }
 
+void ResolutionNotificationController::OnDisplayMetricsChanged(
+    const gfx::Display&, uint32_t) {
+}
+
 void ResolutionNotificationController::OnDisplayConfigurationChanged() {
   if (!change_info_)
     return;