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>
diff --git a/src/images/SkImageEncoderPriv.h b/src/images/SkImageEncoderPriv.h
index 69d45fb..540d930 100644
--- a/src/images/SkImageEncoderPriv.h
+++ b/src/images/SkImageEncoderPriv.h
@@ -11,15 +11,7 @@
 #include "SkImageEncoder.h"
 
 struct SkEncodeOptions {
-    enum class ColorBehavior {
-         // Convert to a linear space before premultiplying or unpremultiplying.
-        kCorrect,
-
-        // Ignore the transfer function when premultiplying or unpremultiplying.
-        kLegacy,
-    };
-
-    ColorBehavior fColorBehavior = ColorBehavior::kLegacy;
+    SkTransferFunctionBehavior fUnpremulBehavior = SkTransferFunctionBehavior::kIgnore;
 };
 
 #ifdef SK_HAS_JPEG_LIBRARY