Add color xform support to SkWebpCodec

src/codec/SkCodecPriv.h

Index: src/codec/SkCodecPriv.h
diff --git a/src/codec/SkCodecPriv.h b/src/codec/SkCodecPriv.h
index 17494074b31306eadea1bf7d17c49e7b104277ff..6edb7514a2e995181beb6ef58a7ec7273c65f4fe 100644
--- a/src/codec/SkCodecPriv.h
+++ b/src/codec/SkCodecPriv.h
@@ -331,4 +331,9 @@ static inline bool needs_color_xform(const SkImageInfo& dstInfo, const SkImageIn
     return !isLegacy && (needsPremul || isF16 || srcDstNotEqual);
 }
 
+static inline SkAlphaType color_xform_alpha_type(SkAlphaType dstAlphaType, SkAlphaType srcAlphaType)

[scroggo, 2016/09/07 20:32:58]

This name seems extra specific, and yet it doesn't tell you what it does. I
don't have a better name off the top of my head though. 

[msarett, 2016/09/07 22:27:41]

Going with "select_alpha_xform".

+{
+    return (kOpaque_SkAlphaType == srcAlphaType) ? kOpaque_SkAlphaType : dstAlphaType;
+}
+
 #endif // SkCodecPriv_DEFINED