Add SkTransferFunctionBehavior flag: Use in codec and encoder

Add SkTransferFunctionBehavior flag: Use in codec and encoder

This is a step towards removing the non-linear blending flag from
SkColorSpace.  The flag on SkColorSpace used to control the premul
behavior - now it is controlled by this option.

BUG=skia:

Change-Id: Ia29bd8c2b0596a93c6aa14332dcd9bd39e388a90
Reviewed-on: https://skia-review.googlesource.com/10008
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>