New helper for creating a color space from another, with linear gamma

include/core/SkColorSpace.h

Index: include/core/SkColorSpace.h
diff --git a/include/core/SkColorSpace.h b/include/core/SkColorSpace.h
index 4b373f48d0155ed21ab8891660124847a762acfb..58095775e4b75e2b9f7a12970f173d5d7886a4f7 100644
--- a/include/core/SkColorSpace.h
+++ b/include/core/SkColorSpace.h
@@ -67,6 +67,11 @@ public:
      */
     static sk_sp<SkColorSpace> NewICC(const void*, size_t);
 
+    /**
+     *  Create an SkColorSpace with the same gamut as this color space, but with linear gamma.
+     */
+    sk_sp<SkColorSpace> makeLinearGamma();
+
     GammaNamed gammaNamed() const { return fGammaNamed; }
 
     /**