Chrome OS: Disable Welcome app by default

This disables Welcome App on selected devices.

Bug: 894095
Change-Id: I3a96e271f669eb2ac6d63d817d49be2838231170
Reviewed-on: https://chromium-review.googlesource.com/c/1287184
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600616}

chrome/browser/chromeos/first_run/first_run.cc

@@ -19,6 +19,7 @@
 #include "chrome/browser/prefs/pref_service_syncable_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
+#include "chrome/browser/ui/ash/tablet_mode_client.h"
 #include "chrome/browser/ui/extensions/app_launch_params.h"
 #include "chrome/browser/ui/extensions/application_launch.h"
 #include "chrome/common/chrome_switches.h"
@@ -75,6 +76,10 @@ void TryLaunchFirstRunDialog(Profile* profile) {
     return;
   }
 
+  // TabletModeClient does not exist in some tests.
+  if (TabletModeClient::Get() && TabletModeClient::Get()->tablet_mode_enabled())
+    return;
+
   if (policy::ProfilePolicyConnectorFactory::GetForBrowserContext(profile)
           ->IsManaged())
     return;