mash: Avoid KeyboardDrivenEventRewriter::GetInstance crash.

chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc b/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
index 63c07a7bce4891abf7d45fcb82b0d96181b8c919..f53ba6d38a29cd223c89eebaec951eb800af9d5b 100644
--- a/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
@@ -303,8 +303,11 @@ void CoreOobeHandler::HandleSkipUpdateEnrollAfterEula() {
 void CoreOobeHandler::HandleUpdateCurrentScreen(const std::string& screen) {
   if (delegate_)
     delegate_->OnCurrentScreenChanged(screen);
-  KeyboardDrivenEventRewriter::GetInstance()->SetArrowToTabRewritingEnabled(
+  // TODO(mash): Support EventRewriterController; see crbug.com/647781
+  if (!chrome::IsRunningInMash()) {
+    KeyboardDrivenEventRewriter::GetInstance()->SetArrowToTabRewritingEnabled(
       screen == WizardController::kEulaScreenName);
+  }
 }
 
 void CoreOobeHandler::HandleEnableHighContrast(bool enabled) {