Add SkSourceGammaTreatment enum so we know how to create mips

include/core/SkImageInfo.h

Index: include/core/SkImageInfo.h
diff --git a/include/core/SkImageInfo.h b/include/core/SkImageInfo.h
index 743ca5948137f0cd7e8d816bc4b2a3c45c84981a..2d89fbf0d6f1102c561600e97279b270bf36f58a 100644
--- a/include/core/SkImageInfo.h
+++ b/include/core/SkImageInfo.h
@@ -176,6 +176,11 @@ enum SkColorProfileType {
     kLastEnum_SkColorProfileType = kSRGB_SkColorProfileType
 };
 
+enum class SkSourceGammaTreatment {
+    kRespect,
+    kIgnore,
+};
+
 /**
  *  Describe an image's dimensions and pixel type.
  *  Used for both src images and render-targets (surfaces).