Plumb flag and settings for BlinkGenPropertyTrees finch trial

This patch plumbs a flag and settings for a BlinkGenPropertyTrees
finch trial. Because we have dependencies on the existing command line
flag (--enable-blink-gen-property-trees), the command line flag has not
been removed in this patch but will be removed in a followup.

Bug: 836884
Change-Id: I73d4c01964b953397d1857a9ee130502792b3d4a
Reviewed-on: https://chromium-review.googlesource.com/c/1355852
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612951}
8 files changed