Add SkSourceGammaTreatment enum so we know how to create mips

gm/texturedomaineffect.cpp

Index: gm/texturedomaineffect.cpp
diff --git a/gm/texturedomaineffect.cpp b/gm/texturedomaineffect.cpp
index 660748873158c095d4d546fc1d86b0cddf28eb14..d72477287d0e54f88551b149ae702df74c52bb26 100644
--- a/gm/texturedomaineffect.cpp
+++ b/gm/texturedomaineffect.cpp
@@ -82,7 +82,8 @@ protected:
         }
 
         SkAutoTUnref<GrTexture> texture(GrRefCachedBitmapTexture(context, fBmp,
-                                                                 GrTextureParams::ClampNoFilter()));
+                                                                 GrTextureParams::ClampNoFilter(),
+                                                                 SkSourceGammaTreatment::kRespect));
         if (!texture) {
             return;
         }