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/gm/image_shader.cpp b/gm/image_shader.cpp
index 522d373..02e6679 100644
--- a/gm/image_shader.cpp
+++ b/gm/image_shader.cpp
@@ -49,7 +49,7 @@
 static sk_sp<SkImage> make_pict_gen(GrContext*, SkPicture* pic, const SkImageInfo& info) {
     return SkImage::MakeFromPicture(sk_ref_sp(pic), info.dimensions(), nullptr, nullptr,
                                     SkImage::BitDepth::kU8,
-                                    SkColorSpace::MakeNamed(SkColorSpace::kSRGB_Named));
+                                    SkColorSpace::MakeSRGB());
 }
 
 static sk_sp<SkImage> make_encode_gen(GrContext* ctx, SkPicture* pic, const SkImageInfo& info) {