Only use direct reasons when querying for fragmentation

This adds onto the other CL (*) that modifies fragmentation +
compositing, and removes another dependency on pre-paint of
compositing.

(*) https://chromium-review.googlesource.com/c/chromium/src/+/2280583

Bug: 1100711

Change-Id: I9b66bc39f4af65746ecc05d834f0e4abf65c04eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2318688
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791568}