Set the unique_event_id when converting from TouchEvent to WebTouchEvent

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index 8c5c6d6893bfbfd4f368e714bfa72c5c94e0759e..40b08d2e091b6457dc0b789cd20c601caf1575a3 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -1223,6 +1223,12 @@ void RenderWidget::OnHandleInputEvent(const blink::WebInputEvent* input_event,
     ack.type = input_event->type;
     ack.state = ack_result;
     ack.latency = swap_latency_info;
+    if (WebInputEvent::isTouchEventType(ack.type)) {
+      const blink::WebTouchEvent& touch =
+          static_cast<const blink::WebTouchEvent&>(*input_event);
+      DCHECK_NE(touch.uniqueTouchEventId, 0UL);
+      ack.unique_touch_event_id = touch.uniqueTouchEventId;
+    }
     scoped_ptr<IPC::Message> response(
         new InputHostMsg_HandleInputEvent_ACK(routing_id_, ack));
     if (rate_limiting_wanted && frame_pending && !is_hidden_) {