Add ThreadChecker for Ozone X11 GPU.

ui/ozone/platform/x11/x11_surface_factory.h

Index: ui/ozone/platform/x11/x11_surface_factory.h
diff --git a/ui/ozone/platform/x11/x11_surface_factory.h b/ui/ozone/platform/x11/x11_surface_factory.h
index 77bee714bb0e9b009b1afd215ff41b1ffa6ad8ba..dfccd5521d30233ccc1d2e6f2c9eb4374358844d 100644
--- a/ui/ozone/platform/x11/x11_surface_factory.h
+++ b/ui/ozone/platform/x11/x11_surface_factory.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/macros.h"
+#include "base/threading/thread_checker.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/ozone/public/gl_ozone.h"
 #include "ui/ozone/public/surface_factory_ozone.h"
@@ -29,6 +30,11 @@ class X11SurfaceFactory : public SurfaceFactoryOzone {
   std::unique_ptr<GLOzone> glx_implementation_;
   std::unique_ptr<GLOzone> egl_implementation_;
 
+  // X11 doesn't care if things being called from different threads if
+  // XInitThreads() was called. However, GBM does care. This will ensure X11
+  // and GBM behave roughly the same.
+  base::ThreadChecker thread_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(X11SurfaceFactory);
 };