Call XRootWindow instead of RootWindow

We have to use the X11 header wrapper since r515373.

BUG=782184

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Icda075c7cc9723f9bd8c667d6ab7e8848e48f8b1
Reviewed-on: https://chromium-review.googlesource.com/911626Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Joone Hur <joone.hur@intel.com>
Cr-Commit-Position: refs/heads/master@{#535956}

gpu/vulkan/tests/native_window_x11.cc

@@ -16,7 +16,7 @@ gfx::AcceleratedWidget CreateNativeWindow(const gfx::Rect& bounds) {
   swa.event_mask = StructureNotifyMask | ExposureMask;
   swa.override_redirect = x11::True;
   XID window = XCreateWindow(
-      display, RootWindow(display, DefaultScreen(display)),  // parent
+      display, XRootWindow(display, DefaultScreen(display)),  // parent
       bounds.x(), bounds.y(), bounds.width(), bounds.height(),
       0,               // border width
       CopyFromParent,  // depth