When APZ traverses a tree using LayerMetricsWrapper, the layer tree
already has its RefLayers connected because of the in-scope
AutoResolveRefLayers. When traversing using the
WebRenderScrollDataWrapper though, this is not the case, and we need to
explicitly jump from one layer tree to another during the walk.
Thankfully we don't require upwards traversal in the tree or this would
be much more complicated.
MozReview-Commit-ID: 8gbvUlzghLx
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 the WebRenderScrollDataWrapper class which is
template-compatible with LayerMetricsWrapper. While the
LayerMetricsWrapper operates on an underlying layer tree, the
WebRenderScrollDataWrapper will simulate a layer tree based on an
underlying WebRenderScrollData object. The class is stubbed out here,
functions will be implemented in subsequent patches.
MozReview-Commit-ID: 9exnFRI6tOW
