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/src/codec/SkGifCodec.cpp b/src/codec/SkGifCodec.cpp
index af0e8bc..2903717 100644
--- a/src/codec/SkGifCodec.cpp
+++ b/src/codec/SkGifCodec.cpp
@@ -106,7 +106,7 @@
 
     const auto imageInfo = SkImageInfo::Make(reader->screenWidth(), reader->screenHeight(),
                                              colorType, alphaType,
-                                             SkColorSpace::MakeNamed(SkColorSpace::kSRGB_Named));
+                                             SkColorSpace::MakeSRGB());
     return new SkGifCodec(encodedInfo, imageInfo, reader.release());
 }