The new struct is in LayersTypes.h, all the rest of the changes are just
replacing existing uint64_t instances with the new LayersId struct.
Note that there is one functional change, in
CompositorBridgeParent::DeallocPWebRenderBridgeParent, where we now
correctly convert the PipelineId to a LayersId before using it to index
into sIndirectLayerTrees, whereas before we were incorrectly just using
the mHandle part of the PipelineId.
MozReview-Commit-ID: GFHZSZiwMrP
--HG--
extra : rebase_source : d2b274f63aaee2ee9bba030297e0a37a19af0d6c
