[BGPT] Don't collect non-animation non-scroll element ids

Collecting non-animation element ids gave compositor wrong information
that they need to be handled by the compositor, causing non-composited
animation (caused by will-change: contents) on composited-layer failed
to start in BGPT mode.

Also add virtual/disable-blink-gen-property-trees/transitions.

Bug: 936912
Change-Id: I3ff64a732920ef884d838064d2d3a005e8a50860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1512765
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641429}