In future, we want to persist a lot more of the information about
primitive instances between display lists. This will allow us to
implement a number of optimizations and improvements to the scene
and frame building code (such as reducing per-frame per-prim work
that is typically mostly redundant, supporting prims other than
pictures that can contain child primitives, unifying and optimizing
primitive dependency updates).
As a step towards that, this patch introduces a picture graph which
is very similar to the idea of the render task graph builder. With
this in place, we're able to run picture updates without using
recursion, and ensuring we update pictures in the correct order
that the pass requires. This will allow us to un-tangle a lot of
the existing scene building, visibility, prep and batching pass
complexity, in order to be able to implement the above.
Differential Revision: https://phabricator.services.mozilla.com/D120191
371f4cd13b