Introduce user customization of external HighDPI mode for 4K monitor.

ash/display/resolution_notification_controller_unittest.cc

Index: ash/display/resolution_notification_controller_unittest.cc
diff --git a/ash/display/resolution_notification_controller_unittest.cc b/ash/display/resolution_notification_controller_unittest.cc
index e351c86ce7115aa4b2c2561f786f06a973d906de..acf1c9c68504cb2711f516c642b552436431f5bc 100644
--- a/ash/display/resolution_notification_controller_unittest.cc
+++ b/ash/display/resolution_notification_controller_unittest.cc
@@ -65,10 +65,16 @@ class ResolutionNotificationControllerTest : public ash::test::AshTestBase {
       const gfx::Size& actual_new_resolution) {
     DisplayManager* display_manager = Shell::GetInstance()->display_manager();
     const DisplayInfo& info = display_manager->GetDisplayInfo(display.id());
+    DisplayMode old_mode(info.size_in_pixel(),
+                         60 /* refresh_rate */,
+                         false /* interlaced */,
+                         false /* native */);
+    DisplayMode new_mode = old_mode;
+    new_mode.size = new_resolution;
     controller()->SetDisplayResolutionAndNotify(
         display.id(),
-        info.size_in_pixel(),
-        new_resolution,
+        old_mode,
+        new_mode,
         base::Bind(&ResolutionNotificationControllerTest::OnAccepted,
                    base::Unretained(this)));