Promote BlinkGenPropertyTrees to experimental

This is another [1] patch promoting BlinkGenPropertyTrees (BGPT) to
experimental. BlinkGenPropertyTrees 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.

[1] Previous attempts at enabling BGPT
Revert Promote BlinkGenPropertyTrees to experimental: https://crrev.com/621669
Promote BlinkGenPropertyTrees to experimental: https://crrev.com/621273
Demote BlinkGenPropertyTrees from experimental to test: https://crrev.com/616506
Promote BGPT to experimental: https://crrev.com/614470
Revert Promote BGPT to experimental: https://crrev.com/603710
Promote BGPT to experimental: https://crrev.com/602150
Revert Promote BGPT to experimental: https://crrev.com/601624
Promote BGPT to experimental: https://crrev.com/601429

Bug: 836884
Change-Id: I59dafd479cd7d23f1cd0f32ea8ca30e56a8836e4
Reviewed-on: https://chromium-review.googlesource.com/c/1407387
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622234}
1 file changed