builds/updates paint property trees.

Consumes the layout/fragment data and produces the four paint property trees (Transform, Clip, Effect, Scroll) for the current frame. These trees encode coordinate systems, clipping, visual effects, and scrolling in a way that can be reused across frames and mapped into cc. (Chromium Git Repositories)

Key idea
It decides when nodes change values vs. structure (important for fast paths like “directly update compositor node”), and prepares the property state used to key paint chunks later. (Chromium Git Repositories)

Hands off to: the actual recording of display items with property‑tree state.