Implement GLX for Ozone X11.

ui/events/platform/x11/x11_event_source_libevent.cc

Index: ui/events/platform/x11/x11_event_source_libevent.cc
diff --git a/ui/events/platform/x11/x11_event_source_libevent.cc b/ui/events/platform/x11/x11_event_source_libevent.cc
index 4d877aea7e54f96dfd2f73136669bc890035c5e8..708ab4104a4d9dc4821b50414e1d6f094950805d 100644
--- a/ui/events/platform/x11/x11_event_source_libevent.cc
+++ b/ui/events/platform/x11/x11_event_source_libevent.cc
@@ -7,6 +7,8 @@
 #include <X11/Xlib.h>
 #include <X11/extensions/XInput2.h>
 
+#include <memory>
+
 #include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
 #include "ui/events/event.h"
@@ -137,6 +139,12 @@ X11EventSourceLibevent::X11EventSourceLibevent(XDisplay* display)
 
 X11EventSourceLibevent::~X11EventSourceLibevent() {}
 
+// static
+X11EventSourceLibevent* X11EventSourceLibevent::GetInstance() {
+  return static_cast<X11EventSourceLibevent*>(
+      PlatformEventSource::GetInstance());
+}
+
 void X11EventSourceLibevent::AddXEventDispatcher(XEventDispatcher* dispatcher) {
   dispatchers_xevent_.AddObserver(dispatcher);
 }