Bugzilla

There are two places where the code that decides whether an element with a transform animation should be pre-rendered so that its the transform animation can run on the compositor, uses `GetCrossDocParentFrame()` in a way that might become invalid with Fission:

  1. [Here](https://searchfox.org/mozilla-central/rev/bf8d5de8528036c09590009720bc172882845b80/layout/painting/nsDisplayList.cpp#7903), where the code is checking for an enclosing mask or clip-path, and decides not to pre-render on that basis. It seems to me that with Fission, if an OOP iframe is inside a mask or clip-path, and an element in the iframe is animated, the code could wrongly decide to pre-render that animation.

 2. [Here](https://searchfox.org/mozilla-central/rev/bf8d5de8528036c09590009720bc172882845b80/layout/painting/nsDisplayList.cpp#7846), where the code is checking for an enclosing `position: sticky` element, and decides not to do **partial pre-render** on that  basis. Again, it seems like with Fission, if an OOP iframe is inside `position: sicky` content, and an element in the iframe is animated, the code could wrongly decide to partially pre-render that animation.

There are two places where the code that decides whether an element with a transform animation should be pre-rendered so that its the transform animation can run on the compositor, uses `GetCrossDocParentFrame()` in a way that might become invalid with Fission:

  1. [Here](https://searchfox.org/mozilla-central/rev/bf8d5de8528036c09590009720bc172882845b80/layout/painting/nsDisplayList.cpp#7903), where the code is checking for an enclosing mask or clip-path, and decides not to pre-render on that basis. It seems to me that with Fission, if an OOP iframe is inside a mask or clip-path, and an element in the iframe is animated, the code could wrongly decide to pre-render that animation.

 2. [Here](https://searchfox.org/mozilla-central/rev/bf8d5de8528036c09590009720bc172882845b80/layout/painting/nsDisplayList.cpp#7846), where the code is checking for an enclosing `position: sticky` element, and decides not to do **partial pre-render** on that  basis. Again, it seems like with Fission, if an OOP iframe is inside `position: sticky` content, and an element in the iframe is animated, the code could wrongly decide to partially pre-render that animation.