Silence libjpeg warnings in SkImageDecoder

We just did the same for libpng (see crrev.com/1512043002), so we
might as well do this here.

SkImageDecoder is deprecated, and SkCodec already has a way to turn
off its messages.

BUG=skia:1649

Review URL: https://codereview.chromium.org/1505953007
1 file changed