SkScaledCodec class

SkScaledCodec class

This class does scaling by using a scanlineDecoder.
getScanlines and skipScanlines are used for y sampling,
the swizzler is used for x sampling

this class is currently only working for png and jpeg images
I will update other Codec types to work soon

For SkJpegCodec to implement width wise swizzling it now
uses a swizzler. I ran performance tests on this change.
Here are the performance test results:
https://docs.google.com/a/google.com/spreadsheets/d/1D7-Q_GXD_dI68LZO005NNvb8Wq2Ee0wEBEPG72671yw/edit?usp=sharing

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/0944100ac89f797714eeae0cf2875e2335ff52ee

Committed: https://skia.googlesource.com/skia/+/d518ea7927f9f4e0ed5b4134d1b4f48243855a47

Review URL: https://codereview.chromium.org/1260673002