Refcount touch tracking ids to prevent freeing them too early.

ui/events/x/events_x.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/event_constants.h"
 
 #include <cmath>
 #include <string.h>
 #include <X11/extensions/XInput.h>
 #include <X11/extensions/XInput2.h>
@@ skipping 626 matching lines @@
     return NULL;
   XEvent* copy = new XEvent;
   *copy = *event;
   return copy;
 }
 
 void ReleaseCopiedNativeEvent(const base::NativeEvent& event) {
   delete event;
 }
 
+void IncrementTouchIdRefCount(const base::NativeEvent& xev) {
+  ui::DeviceDataManagerX11* manager = ui::DeviceDataManagerX11::GetInstance();
+  double tracking_id;
+  if (!manager->GetEventData(
+          *xev, ui::DeviceDataManagerX11::DT_TOUCH_TRACKING_ID, &tracking_id)) {
+    return;
+  }
+
+  ui::TouchFactory* factory = ui::TouchFactory::GetInstance();
+  factory->AcquireSlotForTrackingID(tracking_id);

[sadrul, 2014/07/22 16:49:16]

Should we do this automagically from GetTouchId() when event-type is
TOUCH_PRESSED? It feels bad to add yet-another X11-only event_utils method that
no other platforms need to implement, but it also feels bad for GetTouchId() to
have a side-effect like this. WDYT?

[tdresser, 2014/07/22 20:17:08]

As we just discussed in person, I think there's a lot of value in having the
calls to |IncrementTouchIdRefCount| and |ClearTouchIdIfReleased| in the
constructor and destructor respectively, as it makes it obvious that they match
up.

I'm inclined to go with the current solution.

+}
+
 void ClearTouchIdIfReleased(const base::NativeEvent& xev) {
   ui::EventType type = ui::EventTypeFromNative(xev);
   if (type == ui::ET_TOUCH_CANCELLED ||
       type == ui::ET_TOUCH_RELEASED) {
     ui::TouchFactory* factory = ui::TouchFactory::GetInstance();
     ui::DeviceDataManagerX11* manager = ui::DeviceDataManagerX11::GetInstance();
     double tracking_id;
     if (manager->GetEventData(
         *xev, ui::DeviceDataManagerX11::DT_TOUCH_TRACKING_ID, &tracking_id)) {
       factory->ReleaseSlotForTrackingID(tracking_id);
@@ skipping 118 matching lines @@
   DeviceDataManagerX11::GetInstance()->GetGestureTimes(
       native_event, start_time, end_time);
   return true;
 }
 
 bool IsTouchpadEvent(const base::NativeEvent& event) {
   return DeviceDataManagerX11::GetInstance()->IsTouchpadXInputEvent(event);
 }
 
 }  // namespace ui