BlinkGenPropertyTrees (BGPT) is an incremental step towards making
compositing decisions after the paint lifecycle phase. The primary
changes are to build property trees in blink and send a layer list to
the compositor, rather than building property trees in cc from a layer
tree.

This shifts time (e.g., we now run PaintArtifactCompositor and no
longer run the cc property tree builder) and will likely change
performance benchmarks.

Bug: 836884
Change-Id: I82ef1260baf5e71d9b44f0387bebbc218725b67c
Reviewed-on: https://chromium-review.googlesource.com/c/1363207
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614470}