Only synchronize layers that have rounded corners

We allowed LayerTreeSynchronizer to synchronize square layers in
crrev.com/c/6471644. However, this caused a performance regression in
overview. Synchronizing purely based on intersection with reference
bounds resulted in many layers with rounded corners. Applying rounded
corners to these extra layers has a non-trivial performance impact on
low-end devices.

Bug: b:415049664, b:410480042
Change-Id: Ie8089ac9da2431f61a5d16c5a09b650c4451eaa6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6669752
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Zoraiz Naeem <zoraiznaeem@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1478180}