Chrome OS: suggest user to set up pin in tablet mode only.

Bug: 900233
Change-Id: I7af0c470dc7c1d23b5e7fa8fd0db42d42bf9d03d
Reviewed-on: https://chromium-review.googlesource.com/c/1309140Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604082}

chrome/browser/chromeos/login/screens/discover_screen.cc

@@ -6,6 +6,7 @@
 
 #include "base/logging.h"
 #include "chrome/browser/chromeos/login/screens/discover_screen_view.h"
+#include "chrome/browser/ui/ash/tablet_mode_client.h"
 
 namespace chromeos {
 
@@ -26,7 +27,8 @@ DiscoverScreen::~DiscoverScreen() {
 }
 
 void DiscoverScreen::Show() {
-  if (IsPublicSessionOrEphemeralLogin()) {
+  if (IsPublicSessionOrEphemeralLogin() ||
+      !TabletModeClient::Get()->tablet_mode_enabled()) {
     Finish(ScreenExitCode::DISCOVER_FINISHED);
     return;
   }