login: pass use_flags from handwriting to chrome.

The use flags are also added to "libchromeos-use-flags" in this cl.
https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2331419

BUG=chromium:1054628
TEST='All unit tests passed.

Change-Id: Iccc6b6f6c3ab56da2fd2e9b6980a5683a9669ec0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2331313
Tested-by: Charles . <charleszhao@chromium.org>
Commit-Queue: Charles . <charleszhao@chromium.org>
Reviewed-by: Xinglong Luan <alanlxl@chromium.org>
Reviewed-by: Charles . <charleszhao@chromium.org>
Reviewed-by: Andrew Moylan <amoylan@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
diff --git a/login_manager/chrome_setup.cc b/login_manager/chrome_setup.cc
index 9332876..d5a4101 100644
--- a/login_manager/chrome_setup.cc
+++ b/login_manager/chrome_setup.cc
@@ -430,6 +430,11 @@
 
   if (builder->UseFlagIsSet("enable_heuristic_palm_detection_filter"))
     builder->AddFeatureEnableOverride("EnableHeuristicPalmDetectionFilter");
+
+  if (builder->UseFlagIsSet("ondevice_handwriting"))
+    builder->AddArg("--ondevice_handwriting=use_rootfs");
+  else if (builder->UseFlagIsSet("ondevice_handwriting_dlc"))
+    builder->AddArg("--ondevice_handwriting=use_dlc");
 }
 
 // Adds UI-related flags to the command line.