Steps:

1) Add tabindex=0 to #target0 of pointerevent_touch-action-none-css_touch-manual.html.
2) $ out/Release/content_shell --run-web-tests external/wpt/pointerevents/pointerevent_touch-action-none-css_touch-manual.html

Expected: Test runs fine.

Actual: Test waits, forever, for #btnComplete to be clicked. 

This problem was discovered during https://chromium-review.googlesource.com/c/chromium/src/+/1258331.

The following tests suffer from similar problems resulting in #btnComplete never being clicked.

  external/wpt/pointerevents/extension/pointerevent_touch-action-pan-down-css_touch-manual.html
  external/wpt/pointerevents/extension/pointerevent_touch-action-pan-up-css_touch-manual.html
  external/wpt/pointerevents/pointerevent_touch-action-none-css_touch-manual.html
  external/wpt/pointerevents/pointerevent_touch-action-pan-x-css_touch-manual.html
  external/wpt/pointerevents/pointerevent_touch-action-pan-y-css_touch-manual.html
  external/wpt/pointerevents/pointerevent_touch-action-span-test_touch-manual.html

This problem blocks  Issue 585413  which defaults scrollers' tabindex to 0.

Workaround: Click #btnComplete programmatically from the tests' corresponding pointerevent*-manual-automation.js.