cc: Merge PictureImageLayerImpl and PictureLayerImpl.

This patch doesn't change behavior, but it merges image layer impl with
plain old picture layer impl.

PictureImageLayer still remains, but it creates PictureLayerImpl as
its impl counterpart.

R=enne, danakj
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2094813003
Cr-Commit-Position: refs/heads/master@{#401791}
10 files changed