[cros] Add support for transparent background in sign in screen.

chrome/browser/chromeos/login/webui_login_display_host.cc

Index: chrome/browser/chromeos/login/webui_login_display_host.cc
diff --git a/chrome/browser/chromeos/login/webui_login_display_host.cc b/chrome/browser/chromeos/login/webui_login_display_host.cc
index ea3edca70471a7d97523b47a5de5b5a2391c3aff..a51ef3f0c36ab3badaee6f3fdb9fc380defdd2b8 100644
--- a/chrome/browser/chromeos/login/webui_login_display_host.cc
+++ b/chrome/browser/chromeos/login/webui_login_display_host.cc
@@ -16,6 +16,7 @@
 #include "chrome/browser/chromeos/login/webui_login_view.h"
 #include "chrome/browser/chromeos/login/wizard_controller.h"
 #include "chrome/browser/ui/webui/chromeos/login/oobe_ui.h"
+#include "chrome/common/chrome_switches.h"
 #include "content/public/browser/web_ui.h"
 #include "ui/aura/window.h"
 #include "ui/views/widget/widget.h"
@@ -149,6 +150,8 @@ void WebUILoginDisplayHost::LoadURL(const GURL& url) {
         views::Widget::InitParams::TYPE_WINDOW_FRAMELESS);
     params.bounds = background_bounds();
     params.show_state = ui::SHOW_STATE_FULLSCREEN;
+    if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kEnableNewOobe))
+      params.transparent = true;
     params.parent =
         ash::Shell::GetInstance()->GetContainer(
             ash::internal::kShellWindowId_LockScreenContainer);