[VSync Queue] Plug touch ack to gesture events and flush vsync queue if necessary

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 1ed598061c2dca8f038386555d8b46bf85c0df09..d7536f58465fa9cefd1456b04b1ea80e94b5d461 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -322,6 +322,17 @@ void InputHandlerProxy::HandleInputEventWithLatencyInfo(
   }
 
   if (has_ongoing_compositor_scroll_fling_pinch_) {
+    const auto& gesture_event = ToWebGestureEvent(event_with_callback->event());
+    if (gesture_event.source_device == blink::kWebGestureDeviceTouchscreen &&
+        gesture_event.source_touch_event_dispatch_type ==
+            WebInputEvent::kBlocking) {
+      // Dispatch immediately to reduce latency.
+      compositor_event_queue_->Queue(std::move(event_with_callback),
+                                     tick_clock_->NowTicks());
+      DispatchQueuedInputEvents();
+      return;
+    }
+
     bool needs_animate_input = compositor_event_queue_->empty();
     compositor_event_queue_->Queue(std::move(event_with_callback),
                                    tick_clock_->NowTicks());