[BlinkGenPropertyTrees] Pass all unit tests with BGPT

This patch prepares for promoting BlinkGenPropertyTrees (BGPT) to
experimental by ensuring all unit tests pass. This patch has three
changes:
1) The foreign layer BGPT code has been disabled when SPV2 is on in
LocalFrameView::PaintTree.
2) Some CompositedLayerMapping tests of non-BGPT code have been changed
to only run without BGPT.
3) ScrollingCoordinatorTest of sticky have been updated to look up
sticky constraints on property trees when BGPT is enabled.

Bug: 836902
Change-Id: If5c32b3e02c0908bf505bddbb2d4b635b8049555
Reviewed-on: https://chromium-review.googlesource.com/c/1287169
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601428}
3 files changed