move colorshader into its own .cpp, add color4f variant

include/core/SkShader.h

Index: include/core/SkShader.h
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index 0de53ad65240a839e7889a838cdca2c02561e561..60aa7cd6c9a585c58cd7d1ad6ef531d60f39dcd4 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -17,6 +17,7 @@
 #include "../gpu/GrColor.h"
 
 class SkColorFilter;
+class SkColorSpace;
 class SkPath;
 class SkPicture;
 class SkXfermode;
@@ -375,6 +376,14 @@ public:
      */
     static sk_sp<SkShader> MakeColorShader(SkColor);
 
+    /**
+     *  Create a shader that draws the specified color (in the specified colorspace).
+     *
+     *  This works around the limitation that SkPaint::setColor() only takes byte values, and does
+     *  not support specific colorspaces.
+     */
+    static sk_sp<SkShader> MakeColorShader(const SkColor4f&, sk_sp<SkColorSpace>);
+
     static sk_sp<SkShader> MakeComposeShader(sk_sp<SkShader> dst, sk_sp<SkShader> src,
                                              SkXfermode::Mode);