Bug 168403 – sync-layer-positions-after-scroll fails if run after non-stable-viewport-scroll due to extraneous layouts

• Component: Tools / Tests
• Status: NEW

[Tim Horton]

Created attachment 301685 [details]
logging

If you remove the viewport meta tag added to sync-layer-positions-after-scroll in https://bugs.webkit.org/show_bug.cgi?id=168376, and then:

run-webkit-tests -v --ios-simulator --no-retry-failures scrollingcoordinator/ios

You will see sync-layer-positions-after-scroll fail. If you run it by itself, it does not.

The attached logging is from a debugging session with smfr. For some reason, we get into a state where we are calling setViewportConstrainedObjectsNeedLayout repeatedly during scrolling with a fixedpos element, which breaks various assumptions of the test (causing the layer position to get set, and clearing the approximatePosition).

It seems like this is related to changing scale or useFlexibleViewport, or something, and smfr says he's seen it before.