Re-land of "converted GrSimpleTextureEffect to sksl"

This reverts commit baf981f71614e7a2fbe6af2726e65126d431ed8e.

Bug: skia:
Change-Id: I36f6bfb616f1ec2b89043e3a6f7cbdf473bc9588
Reviewed-on: https://skia-review.googlesource.com/22369
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/sksl_fp.include b/src/sksl/sksl_fp.include
index 566e441..0d8d99d 100644
--- a/src/sksl/sksl_fp.include
+++ b/src/sksl/sksl_fp.include
@@ -20,4 +20,6 @@
 layout(builtin=10004) out vec4 sk_OutColor;
 layout(builtin=10005) vec2[] sk_TransformedCoords2D;
 layout(builtin=10006) sampler2D[] sk_TextureSamplers;
+
+vec4 COLORSPACE(vec4 color, colorSpaceXform colorSpace);
 )