src/sksl/sksl_pipeline.inc - skia - Git at Google

 STRINGIFY(
     layout(builtin=15) float4 sk_FragCoord;
     half4 sample(fragmentProcessor fp, float2 coords);
     half4 sample(fragmentProcessor fp, float3x3 transform);
 )
	STRINGIFY(
	layout(builtin=15) float4 sk_FragCoord;
	half4 sample(fragmentProcessor fp, float2 coords);
	half4 sample(fragmentProcessor fp, float3x3 transform);
	)