Touch events sent to a page can be either blocking or non-blocking. A blocking touch event means that the page calls preventDefault() to prevent the browser from turning the touch into a scroll. TouchMove events start out blocking until the first event in a sequence isn’t preventDefaulted and causes scrolling. Chromium currently reverts the touchevent stream back to blocking so that pages can override browser default overscrolling behavior. This feature causes overscrolling to be non-blocking.
Docs: http://crbug.com/1072364
Samples: https://bokand.github.io/block-overscroll.html
Explainers: None, this was discovered as a performance (janky scrolls) issue and we believe this to be the proper fix.