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.

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