Make the native select menu work on Linux touch screen

ui/events/devices/x11/touch_factory_x11.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/devices/x11/touch_factory_x11.h"
 
 #include <X11/Xatom.h>
 #include <X11/cursorfont.h>
 #include <X11/extensions/XInput.h>
 #include <X11/extensions/XInput2.h>
@@ skipping 142 matching lines @@
 }
 
 bool TouchFactory::ShouldProcessXI2Event(XEvent* xev) {
   DCHECK_EQ(GenericEvent, xev->type);
   XIEvent* event = static_cast<XIEvent*>(xev->xcookie.data);
   XIDeviceEvent* xiev = reinterpret_cast<XIDeviceEvent*>(event);
 
   if (event->evtype == XI_TouchBegin ||
       event->evtype == XI_TouchUpdate ||
       event->evtype == XI_TouchEnd) {
-    return !touch_events_disabled_ && IsTouchDevice(xiev->deviceid);
+    // Since SetupXI2ForXWindow() selects events from all devices, for a
+    // touchscreen attached to a master pointer device, X11 sends two
+    // events for each touch: one from the slave (deviceid == the id of
+    // the touchscreen device), and one from the master (deviceid == the
+    // id of the master pointer device). Instead of processing both
+    // events, discard the event that comes from the slave, and only
+    // allow processing the event coming from the master.
+    // For a 'floating' touchscreen device, X11 sends only one event for
+    // each touch, with both deviceid and sourceid set to the id of the
+    // touchscreen device.
+    bool is_from_slave_device = !touch_device_list_[xiev->deviceid] &&
+        (xiev->sourceid == xiev->deviceid);

[sadrul, 2015/03/11 07:43:49]

Just one more nit:

  bool is_from_master_or_float = touch_device_list_[xiev->deviceid];
  bool is_from_slave_device = !is_from_master_or_float &&
      xiev->sourceid == xiev->deviceid;

+    return !touch_events_disabled_ &&
+           IsTouchDevice(xiev->deviceid) &&
+           !is_from_slave_device;
   }
 
   // Make sure only key-events from the virtual core keyboard are processed.
   if (event->evtype == XI_KeyPress || event->evtype == XI_KeyRelease) {
     return (virtual_core_keyboard_device_ < 0) ||
            (virtual_core_keyboard_device_ == xiev->deviceid);
   }
 
   if (event->evtype != XI_ButtonPress &&
       event->evtype != XI_ButtonRelease &&
@@ skipping 150 matching lines @@
       if (ptr[0] || ptr[1])
         touchscreen_ids_.insert(std::make_pair(ptr[0], ptr[1]));
     }
     XFree(prop_return);
   }
 
   XCloseDevice(display, device);
 }
 
 }  // namespace ui