Disable tonal color for shadowutils GMs

Change-Id: Id64ad0cdf1378d38940cfe0d8335ce4d5776abd2
Reviewed-on: https://skia-review.googlesource.com/74361
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

gm/shadowutils.cpp

@@ -15,6 +15,7 @@ void draw_shadow(SkCanvas* canvas, const SkPath& path, int height, SkColor color
                  SkScalar lightR, bool isAmbient, uint32_t flags) {
     SkScalar ambientAlpha = isAmbient ? .5f : 0.f;
     SkScalar spotAlpha = isAmbient ? 0.f : .5f;
+    flags |= SkShadowFlags::kDisableTonalColor_ShadowFlag;
     SkShadowUtils::DrawShadow(canvas, path, height, lightPos, lightR, ambientAlpha, spotAlpha,
                               color, flags);
 }