Add sRGB 8888 colortype

A color type that linearizes just after loading, and re-encodes to sRGB
just before storing, mimicking the GPU formats that work the same way.

  - No mipmap support
  - No SkPngEncoder support (HashAndEncode's .pngs are ok, though?)
  - Needs better testing

This is a re-creation of

Change-Id: I4739c2280211e7176aae98ba0a8476a7fe5efa72
Commit-Queue: Brian Osman <>
Reviewed-by: Brian Salomon <>
32 files changed