Handle late OnSessionEnded() calls

A TouchModeChanged() call may happen just after a session ends, but
just before the associated OnSessionEnded() call. This caused a
DCHECK. Handle this case by ignoring it.

Fixed: 1165462
Change-Id: Id8c8a52acd94fef6a34a5349693af7caa9c570d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2622529Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845287}

chrome/browser/metrics/desktop_session_duration/touch_mode_stats_tracker.cc

@@ -65,8 +65,14 @@ void TouchModeStatsTracker::OnSessionEnded(base::TimeDelta session_length,
                                            base::TimeTicks session_end) {
   // If we end in touch mode, we must count the time from
   // last_touch_mode_switch_in_session_ to session_end.
-  if (touch_ui_controller_->touch_ui()) {
-    DCHECK_GE(session_end, last_touch_mode_switch_in_session_);
+  //
+  // |session_end| may be slightly less than
+  // |last_touch_mode_switch_in_session_| because an OnSessionEnded()
+  // call may happen slightly after the session end time. Assuming the
+  // difference is small, the touch mode time left unaccounted for is small.
+  // Accept this error and ignore this time. See crbug.com/1165462.
+  if (touch_ui_controller_->touch_ui() &&
+      session_end >= last_touch_mode_switch_in_session_) {
     touch_mode_duration_in_session_ +=
         session_end - last_touch_mode_switch_in_session_;
   }