Display list management

Hi,
I'm trying to understand what is the functionality of the dlm module in 
Chromium.
Scanning the cr tree I found there are rather limited uses of it, 
actually three SPUs: replicate, tilesort and expando

The first two fan-out one gl stream to several renderers, so I infer 
that dlm is used to keep track of the display lists in these one-to-many 
environments.

What about expando? The description indicates it "unfolds" a display 
list. This will impact performance...in which scenario is this SPU 
useful? debugging? does it have to do with correctness/conformance?

Thanks a lot to anyone who can shed some light on this :)
Andres

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