Open this page: http://output.jsbin.com/puzegal

Use the dev tool to go into device emulator, select a mobile device such as pixel xl. Wait until the border is red, now fling on the x direction. Observe that the scroller starts moving only when the border is not red.

What's happening:
The scroller has a passive event listener for touchstart and touchmove, which means the gesture that we have should be non-blocking. Red border indicates that the main thread is janky. So the scroller should still move even if the border is red.