Push much of the SkColorSpace_Base interface up to SkColorSpace

Some pieces still remain, but the next step looks less mechanical,
so I wanted to land this piece independently.

Bug: skia:
Change-Id: Ie63afcfa08af2f6e4996911fa2225c43441dbfb2
Reviewed-on: https://skia-review.googlesource.com/84120
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/gm/color4f.cpp b/gm/color4f.cpp
index 36850a1..5f281e9 100644
--- a/gm/color4f.cpp
+++ b/gm/color4f.cpp
@@ -96,7 +96,7 @@
     canvas->translate(10, 10);
 
     auto srgb = SkColorSpace::MakeSRGB();
-    auto spin = as_CSB(srgb)->makeColorSpin(); // RGB -> GBR
+    auto spin = srgb->makeColorSpin(); // RGB -> GBR
 
     const SkColor4f colors[] {
         { 1, 0, 0, 1 },