x11: Use scoped_ptr<> for X11 objects where it makes sense.

ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc

Index: ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc
diff --git a/ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc b/ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc
index 6b14045ef3971755faa9211b6399e2dd32bee03f..9cf10d43e04667d4ab4f68ad179a25cadaa0dac2 100644
--- a/ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc
+++ b/ash/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc
@@ -76,8 +76,9 @@ ScopedDisableInternalMouseAndKeyboardX11::
       static_cast<ui::DeviceDataManagerX11*>(
           ui::DeviceDataManager::GetInstance());
   if (device_data_manager->IsXInput2Available()) {
-    XIDeviceList xi_dev_list = ui::DeviceListCacheX11::GetInstance()->
-        GetXI2DeviceList(gfx::GetXDisplay());
+    const XIDeviceList& xi_dev_list =
+        ui::DeviceListCacheX11::GetInstance()->GetXI2DeviceList(
+            gfx::GetXDisplay());
     for (int i = 0; i < xi_dev_list.count; ++i) {
       std::string device_name(xi_dev_list[i].name);
       base::TrimWhitespaceASCII(device_name, base::TRIM_TRAILING, &device_name);