WPT details: As the spec gives a lot of leeway to user agents, we don’t believe a test is appropriate at this point. However this behaviour does now have a unittest in chrome. If this behaviour became part of the spec a test could be appropriate.
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