The sources provide an exhaustive technical explanation of the cc::LayerImpl class, which is the core representation of a visual element within Chromium's multi-threaded rendering pipeline. These layers exist exclusively on the compositor thread and are created or updated during the commit process from the main thread, operating in a layer list mode that leverages four types of property trees (Transform, Clip, Effect, Scroll) to manage hierarchical relationships and properties instead of traditional parent-child pointers. The layer objects are crucial for the performance optimization of drawing frames, as they store geometry, manage input regions for hit testing, and are instrumental in the asynchronous tiling and rasterization system (especially through PictureLayerImpl) and the three-tree model (Active, Pending, Recycle) used for frame staging and reuse. Ultimately, each layer's state is used in the quad generation step to produce a viz::CompositorFrame for the display compositor.
