Added kSRGBLinear_Named color space, along with tests

gm/colorspacexform.cpp

Index: gm/colorspacexform.cpp
diff --git a/gm/colorspacexform.cpp b/gm/colorspacexform.cpp
index 7e3285efbd57c4236d63e731db0bea4e009b01aa..34abdc4b79e7f828cbec7bde81892d6fdb322891 100644
--- a/gm/colorspacexform.cpp
+++ b/gm/colorspacexform.cpp
@@ -60,8 +60,7 @@ protected:
 
             canvas->save();
             for (int i = 0; i < kNumColors; i++) {
-                sk_sp<SkColorSpace> space =
-                        SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named)->makeLinearGamma();
+                sk_sp<SkColorSpace> space = SkColorSpace::NewNamed(SkColorSpace::kSRGBLinear_Named);
                 sk_sp<SkShader> s = SkShader::MakeColorShader(colors[i], space);
                 SkPaint paint;
                 paint.setShader(s);