SkColorSpace: remove named API, add gamut API

Reland from: https://skia-review.googlesource.com/c/8021/

BUG=skia:

Change-Id: I18985f130587b15fccbc86b76b2bb5c49ba5ba8a
Reviewed-on: https://skia-review.googlesource.com/8136
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
diff --git a/bench/GrMipMapBench.cpp b/bench/GrMipMapBench.cpp
index 56b66ce..2037495 100644
--- a/bench/GrMipMapBench.cpp
+++ b/bench/GrMipMapBench.cpp
@@ -36,7 +36,7 @@
             if (nullptr == context) {
                 return;
             }
-            auto srgb = SkColorSpace::MakeNamed(SkColorSpace::kSRGB_Named);
+            auto srgb = SkColorSpace::MakeSRGB();
             SkImageInfo info = SkImageInfo::Make(fW, fH, kN32_SkColorType, kPremul_SkAlphaType,
                                                  srgb);
             fSurface = SkSurface::MakeRenderTarget(context, SkBudgeted::kNo, info);