X11: Avoid round-tripping to get the cursor position

ui/events/platform/x11/x11_event_source.cc

Index: ui/events/platform/x11/x11_event_source.cc
diff --git a/ui/events/platform/x11/x11_event_source.cc b/ui/events/platform/x11/x11_event_source.cc
index a49cda90a74ed351b5a6c367e8120fa359dbf70c..268b2cb2e9bd66311f843a1982fe8eff8a887935 100644
--- a/ui/events/platform/x11/x11_event_source.cc
+++ b/ui/events/platform/x11/x11_event_source.cc
@@ -97,6 +97,7 @@ X11EventSource::X11EventSource(X11EventSourceDelegate* delegate,
     : delegate_(delegate),
       display_(display),
       event_timestamp_(CurrentTime),
+      dispatching_event_(nullptr),
       dummy_initialized_(false),
       continue_stream_(true) {
   DCHECK(!instance_);
@@ -201,12 +202,14 @@ void X11EventSource::ExtractCookieDataDispatchEvent(XEvent* xevent) {
     have_cookie = true;
   }
 
+  dispatching_event_ = xevent;
   event_timestamp_ = ExtractTimeFromXEvent(*xevent);
 
   delegate_->ProcessXEvent(xevent);

[sadrul, 2016/10/07 02:12:51]

This can trigger a nested message loop, which means |dispatching_event_| will
not be reset until the nested message loop ends. So if some code tries to get
the current cursor location (from a timeout task, for example), then it will get
stale information.

[Tom (Use chromium acct), 2016/10/07 21:13:18]

done: added a stack of events to handle this.

   PostDispatchEvent(xevent);
 
   event_timestamp_ = CurrentTime;
+  dispatching_event_ = nullptr;
 
   if (have_cookie)
     XFreeEventData(xevent->xgeneric.display, &xevent->xcookie);