X11: Better timestamp handling for _NET_ACTIVE_WINDOW

ui/events/platform/x11/x11_event_source.h

Index: ui/events/platform/x11/x11_event_source.h
diff --git a/ui/events/platform/x11/x11_event_source.h b/ui/events/platform/x11/x11_event_source.h
index 5b74e6357c8ed7ec8f33d634cd6d9604cab4e1c4..99594e6a2371595fba900e6bd7f2eda3ecea4ef3 100644
--- a/ui/events/platform/x11/x11_event_source.h
+++ b/ui/events/platform/x11/x11_event_source.h
@@ -16,6 +16,7 @@
 using Time = unsigned long;
 using XEvent = union _XEvent;
 using XID = unsigned long;
+using XWindow = unsigned long;
 
 namespace ui {
 
@@ -62,6 +63,10 @@ class EVENTS_EXPORT X11EventSource {
   XDisplay* display() { return display_; }
   Time last_seen_server_time() const { return last_seen_server_time_; }
 
+  // Explicitly asks the X11 server for the current timestamp, and updates
+  // |last_seen_server_time| with this value.
+  Time UpdateLastSeenServerTime();
+
   void StopCurrentEventStream();
   void OnDispatcherListChanged();
 
@@ -85,6 +90,11 @@ class EVENTS_EXPORT X11EventSource {
   // The last timestamp seen in an XEvent.
   Time last_seen_server_time_;
 
+  // State necessary for UpdateLastSeenServerTime
+  bool dummy_initialized_;
+  XWindow dummy_window_;
+  XAtom dummy_atom_;
+
   // Keeps track of whether this source should continue to dispatch all the
   // available events.
   bool continue_stream_ = true;