This is a tracking bug for a Q2 2018 OKR.

Summary:

1. Provide list of GraphicsLayers that draw content to PaintArtifactCompositor.
2. Use PaintArtifactCompositor to generate cc property trees and render surfaces.
3. Put cc in layer list mode (LayerTreeSettings::use_layer_lists) (this also turns off
cc::PropertyTreeBuilder).