Bug 1837226 part 3: Make nsBaseWidget::SwipeFinished destroy its SwipeTracker before clearing pointer. r=hiro

This new call should generally be a no-op, since we already un-register before
we get here, i.e. before we call SwipeFinished on the widget. This new call is
just to be extra-sure we're unregistered.  With this change, nsBaseWidget is
now consistent about calling Destroy before clearing its mSwipeTracker pointer.

Depends on D180240

Differential Revision: https://phabricator.services.mozilla.com/D180241

widget/nsBaseWidget.cpp

@@ -2229,7 +2229,10 @@ nsresult nsBaseWidget::AsyncEnableDragDrop(bool aEnable) {
       kAsyncDragDropTimeout, EventQueuePriority::Idle);
 }
 
-void nsBaseWidget::SwipeFinished() { mSwipeTracker = nullptr; }
+void nsBaseWidget::SwipeFinished() {
+  mSwipeTracker->Destroy();
+  mSwipeTracker = nullptr;
+}
 
 void nsBaseWidget::ReportSwipeStarted(uint64_t aInputBlockId,
                                       bool aStartSwipe) {