SkLS accepts nullptr for pointer args, handles alpha accurately, has new GM

src/core/SkNormalSource.h

Index: src/core/SkNormalSource.h
diff --git a/src/core/SkNormalSource.h b/src/core/SkNormalSource.h
index 7517770800190e7bb851cba8886786ba129be07d..e46e2dae34cc84d5fdf0e2877f2c21968f1fff13 100644
--- a/src/core/SkNormalSource.h
+++ b/src/core/SkNormalSource.h
@@ -65,6 +65,10 @@ public:
     */
     static sk_sp<SkNormalSource> MakeFromNormalMap(sk_sp<SkShader> map, const SkMatrix& ctm);
 
+    /** Returns a normal source that provides straight-up normals only (0, 0, 1).
+    */
+    static sk_sp<SkNormalSource> MakeFlat();
+
     SK_DEFINE_FLATTENABLE_TYPE(SkNormalSource)
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 };