default SkPixelSerializer

Add SkImageEncoder::EncodeData(const SkPixmap&, ...) function.

Add SkImageEncoder::CreatePixelSerializer() to return a
PixelSerializer that calls into SkImageEncoder::EncodeData.

SkImage::encode() make use of SkImageEncoder::CreatePixelSerializer.

Committed: https://skia.googlesource.com/skia/+/b0bd1516bff3f5afcbfd615e805867531657811b

Review URL: https://codereview.chromium.org/1507123002
7 files changed