Rename SkColorSpace::GammaNamed to SkColorSpace::RenderTargetGamma

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2319293002

Review-Url: https://codereview.chromium.org/2319293002
diff --git a/gm/color4f.cpp b/gm/color4f.cpp
index b3be57b..2f86842 100644
--- a/gm/color4f.cpp
+++ b/gm/color4f.cpp
@@ -112,8 +112,8 @@
         sk_sp<SkShader> shaders[] {
             SkShader::MakeColorShader(c4, nullptr),
             SkShader::MakeColorShader(c4, SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named)),
-            SkShader::MakeColorShader(c4, SkColorSpace::NewRGB(SkColorSpace::kLinear_GammaNamed,
-                                                               mat)),
+            SkShader::MakeColorShader(c4,
+                    SkColorSpace::NewRGB(SkColorSpace::kLinear_RenderTargetGamma, mat)),
         };
 
         canvas->save();