APNG support ( issue 437662 ) is in progress at https://codereview.chromium.org/2618633004/

That patch does not address the following line from the spec (https://wiki.mozilla.org/APNG_Specification#Error_Handling):

""It is strongly recommended that when any error is encountered decoders should discard all subsequent frames, stop the animation, and revert to displaying the default image."

If an error is seen before the IDAT, the above patch does revert to displaying the default image. But if errors occur after IDAT, they are treated as failures (draw nothing). Instead, we should revert to showing the default image. This may require more invasive changes, since the client may have already cached frames and have an idea about how many there should be.