src/sksl/sksl_frag.include - skia - Git at Google

 STRINGIFY(

 // defines built-in interfaces supported by SkiaSL fragment shaders

 layout(builtin=15) in vec4 gl_FragCoord;

 )
	STRINGIFY(

	// defines built-in interfaces supported by SkiaSL fragment shaders

	layout(builtin=15) in vec4 gl_FragCoord;

	)