Add PlatformWindow/Event related code for Ozone X11.

ui/events/x/events_x_utils.h

Index: ui/events/x/events_x_utils.h
diff --git a/ui/events/x/events_x_utils.h b/ui/events/x/events_x_utils.h
index 15c4e387f82e7f140b79f491d0f9232abde8f299..9b570dd56097e1b84b8e5484e784a30dc34d2fef 100644
--- a/ui/events/x/events_x_utils.h
+++ b/ui/events/x/events_x_utils.h
@@ -11,21 +11,25 @@
 #include "ui/events/event_constants.h"
 #include "ui/events/x/events_x_export.h"
 #include "ui/gfx/geometry/point.h"
+#include "ui/gfx/x/x11_types.h"
 
 typedef union _XEvent XEvent;
 
 namespace ui {
 
-// Get the EventType from a XEvent.
+// Gets the XID of XWindow from a XEvent.
+EVENTS_X_EXPORT XID XWindowFromXEvent(const XEvent& xev);
+
+// Gets the EventType from a XEvent.
 EVENTS_X_EXPORT EventType EventTypeFromXEvent(const XEvent& xev);
 
-// Get the EventFlags from a XEvent.
+// Gets the EventFlags from a XEvent.
 EVENTS_X_EXPORT int EventFlagsFromXEvent(const XEvent& xev);
 
-// Get the timestamp from a XEvent.
+// Gets the timestamp from a XEvent.
 EVENTS_X_EXPORT base::TimeDelta EventTimeFromXEvent(const XEvent& xev);
 
-// Get the location from a XEvent.  The coordinate system of the resultant
+// Gets the location from a XEvent.  The coordinate system of the resultant
 // |Point| has the origin at top-left of the "root window".  The nature of
 // this "root window" and how it maps to platform-specific drawing surfaces is
 // defined in ui/aura/root_window.* and ui/aura/window_tree_host*.