Reland "Revert "Make SKP deserialize null instead of PNG images by default.""

This reverts commit b78c91996051d250b6a2946a7b6f14719e014d57.

Reason for revert: Possible cause of https://crbug.com/1485891

Original change's description:
> Revert "Revert "Make SKP deserialize null instead of PNG images by default.""
>
> This reverts commit 2d295711337cf6fcbf66dfc90af39d4188999108.
>
> Change-Id: I158484509c1d067cbebdc99f97e42ff734fa855a
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/755548
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Kevin Lubick <kjlubick@google.com>

Change-Id: Ifb716927460a8ab6a03dafc168d1eb1eb230fea7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/759268
Owners-Override: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Kevin Lubick <kjlubick@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
21 files changed