cc : Replace FindLayerInSubtree calls with LayerById

This CL also removes dead code in layer_impl.h

BUG=557194
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1836913002

Cr-Commit-Position: refs/heads/master@{#383557}
5 files changed