x11: Use kernel timestamps for touch events (if available).

ui/base/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/base/events.h"
 
 #include <string.h>
 #include <X11/extensions/XInput.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xlib.h>
@@ skipping 754 matching lines @@
       return base::TimeDelta::FromMilliseconds(native_event->xkey.time);
     case ButtonPress:
     case ButtonRelease:
       return base::TimeDelta::FromMilliseconds(native_event->xbutton.time);
       break;
     case MotionNotify:
       return base::TimeDelta::FromMilliseconds(native_event->xmotion.time);
       break;
     case GenericEvent: {
       double start, end;
+      float touch_timestamp;
       if (GetGestureTimes(native_event, &start, &end)) {
         // If the driver supports gesture times, use them.
         return base::TimeDelta::FromMicroseconds(end * 1000000);
+      } else if (ValuatorTracker::GetInstance()->ExtractValuator(*native_event,
+                 ValuatorTracker::VAL_TOUCH_RAW_TIMESTAMP, &touch_timestamp)) {
+        return base::TimeDelta::FromMicroseconds(touch_timestamp * 1000000);
       } else {
         XIDeviceEvent* xide =
             static_cast<XIDeviceEvent*>(native_event->xcookie.data);
         return base::TimeDelta::FromMilliseconds(xide->time);
       }
       break;
     }
   }
   NOTREACHED();
   return base::TimeDelta();
@@ skipping 242 matching lines @@
     noop->xclient.format = 8;
     DCHECK(!noop->xclient.display);
   }
   // Make sure we use atom from current xdisplay, which may
   // change during the test.
   noop->xclient.message_type = GetNoopEventAtom();
   return noop;
 }
 
 }  // namespace ui