partial switch over to sp usage of shaders

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1776973003

Review URL: https://codereview.chromium.org/1776973003
diff --git a/gm/drawbitmaprect.cpp b/gm/drawbitmaprect.cpp
index c90ac2e..7ee2271 100644
--- a/gm/drawbitmaprect.cpp
+++ b/gm/drawbitmaprect.cpp
@@ -70,12 +70,12 @@
     SkRect rect = SkRect::MakeWH(wScalar, hScalar);
     SkMatrix mat = SkMatrix::I();
     for (int i = 0; i < 4; ++i) {
-        paint.setShader(SkGradientShader::CreateRadial(
+        paint.setShader(SkGradientShader::MakeRadial(
                         pt, radius,
                         colors, pos,
                         SK_ARRAY_COUNT(colors),
                         SkShader::kRepeat_TileMode,
-                        0, &mat))->unref();
+                        0, &mat));
         canvas->drawRect(rect, paint);
         rect.inset(wScalar / 8, hScalar / 8);
         mat.postScale(SK_Scalar1 / 4, SK_Scalar1 / 4);