When decoding a paletted PNG, require that a PLTE chunk is seen before the first IDAT chunk.
When decoding a paletted PNG, require that a PLTE chunk is seen before
the first IDAT chunk.

R=rsc
APPROVED=rsc
DELTA=7  (2 added, 0 deleted, 5 changed)
OCL=34583
CL=34585
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go