Linux dbg is also unhappy:
https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20%28dbg%29/builds/7843/steps/webkit_tests/logs/stdio
15:42:55.875 23121 [33929/41616] imported/wpt/pointerevents/pointerevent_button_attribute_mouse-manual.html failed unexpectedly (-expected.txt was missing, -expected.png was missing)
15:42:55.874 23177 worker/7 imported/wpt/pointerevents/pointerevent_button_attribute_mouse-manual.html failed:
15:42:55.874 23177 worker/7 -expected.txt was missing
15:42:55.874 23177 worker/7 -expected.png was missing
Comment 1 by nzolghadr@chromium.org
, May 25 2016