hide setImageFilter(ptr)

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4184

Change-Id: Iad792cfdf54087ad4c424fd268559c162a9a5f5c
Reviewed-on: https://skia-review.googlesource.com/4184
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 9bebb5c..d3876b1 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -481,7 +481,7 @@
              *      draw onto the previous layer using the xfermode from the original paint.
              */
             SkPaint tmp;
-            tmp.setImageFilter(fPaint->getImageFilter());
+            tmp.setImageFilter(sk_ref_sp(fPaint->getImageFilter()));
             tmp.setBlendMode(fPaint->getBlendMode());
             SkRect storage;
             if (rawBounds) {