[1.5.4] Fix an issue.

Runtime/gestures/binding.cs

             }
 
             HitTestResult hitTestResult = null;
-            if (evt is PointerDownEvent || evt is PointerSignalResolver) {
+            if (evt is PointerDownEvent || evt is PointerSignalEvent) {
                 D.assert(!this._hitTests.ContainsKey(evt.pointer));
                 hitTestResult = new HitTestResult();
                 this.hitTest(hitTestResult, evt.position);