Partly fix performance regression of crrev.com/835038

crrev.com/835038 added check for whether an element animating transform
is identity-or-translation. This added slight overhead during
compositing update with large amount of animating elements.

This CL reduces the overhead by calling CanPropagateSubpixelAccumulation()
only if the subpixel accumulation is not zero.

Bug: 1157047
Change-Id: Ic1c0c9732c0d82360c3778a5b5b129c2e3f01ae1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2585504
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835974}