This puts all the other things that APZ needs into the
WebRenderScrollData object. The main exception is the scroll clip - I'm
not totally sure how that will be handled yet, so for now we just return
no clip from WebRenderScrollDataWrapper.
MozReview-Commit-ID: 1IhGhSFiPYi
This mainly implements the GetLastChild and GetPreviousSibling functions
in the WebRenderScrollDataWrapper, and adds helper functions that are
needed to make that possible. This allows the WebRenderScrollDataWrapper
to simulate a full "LayerMetrics" tree using the information in the
underlying WebRenderScrollData object.
MozReview-Commit-ID: K82Ud2gAo8K
This adds a WebRenderScrollData class (which contains a list of
WebRenderLayerScrollData objects, among other things), and adds it to
the DPEnd/DPSyncEnd messages sent across PWebRenderBridge. These classes are
skeletons for now (more stuff will be added to them in future patches).
MozReview-Commit-ID: 9duxwlUpdu7
