cros login: Forward HW overlays flags.

Forward drm and overlay command line flags for Guest session.

Bug: 
Change-Id: Ie9b167aefc7ab813116913534653903ccf5e323f
Reviewed-on: https://chromium-review.googlesource.com/572583Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487332}

chrome/browser/chromeos/login/chrome_restart_request.cc

@@ -125,6 +125,8 @@ void DeriveCommandLine(const GURL& start_url,
     ::switches::kEnableViewport,
     ::switches::kEnableZeroCopy,
 #if defined(USE_OZONE)
+    ::switches::kEnableDrmAtomic,
+    ::switches::kEnableHardwareOverlays,
     ::switches::kExtraTouchNoiseFiltering,
     ::switches::kEdgeTouchFiltering,
 #endif