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/giantbitmap.cpp b/gm/giantbitmap.cpp
index 4005359..e1ba737 100644
--- a/gm/giantbitmap.cpp
+++ b/gm/giantbitmap.cpp
@@ -104,9 +104,7 @@
             SkScalar scale = 11*SK_Scalar1/12;
             m.setScale(scale, scale);
         }
-        SkShader* s = SkShader::CreateBitmapShader(getBitmap(), fMode, fMode, &m);
-
-        paint.setShader(s)->unref();
+        paint.setShader(SkShader::MakeBitmapShader(getBitmap(), fMode, fMode, &m));
         paint.setFilterQuality(fDoFilter ? kLow_SkFilterQuality : kNone_SkFilterQuality);
 
         canvas->translate(SkIntToScalar(50), SkIntToScalar(50));