Add SkSourceGammaTreatment enum so we know how to create mips

src/effects/gradients/SkLinearGradient.cpp

Index: src/effects/gradients/SkLinearGradient.cpp
diff --git a/src/effects/gradients/SkLinearGradient.cpp b/src/effects/gradients/SkLinearGradient.cpp
index 7752aac51d5431d281c11aac1ae94ac48d287928..cd55673dc982e76e1ce0a2097af4db4b06301178 100644
--- a/src/effects/gradients/SkLinearGradient.cpp
+++ b/src/effects/gradients/SkLinearGradient.cpp
@@ -418,7 +418,8 @@ const GrFragmentProcessor* GrLinearGradient::TestCreate(GrProcessorTestData* d)
     int colorCount = RandomGradientParams(d->fRandom, colors, &stops, &tm);
     auto shader = SkGradientShader::MakeLinear(points, colors, stops, colorCount, tm);
     const GrFragmentProcessor* fp = shader->asFragmentProcessor(d->fContext,
-        GrTest::TestMatrix(d->fRandom), NULL, kNone_SkFilterQuality);
+        GrTest::TestMatrix(d->fRandom), NULL, kNone_SkFilterQuality,
+        SkSourceGammaTreatment::kRespect);
     GrAlwaysAssert(fp);
     return fp;
 }
@@ -445,7 +446,8 @@ const GrFragmentProcessor* SkLinearGradient::asFragmentProcessor(
                                                  GrContext* context,
                                                  const SkMatrix& viewm,
                                                  const SkMatrix* localMatrix,
-                                                 SkFilterQuality) const {
+                                                 SkFilterQuality,
+                                                 SkSourceGammaTreatment) const {
     SkASSERT(context);
 
     SkMatrix matrix;