remove unused mode parameter from SkMergeImageFilter

Bug: skia:
Change-Id: Iaa46aaef130a337987c3528685f59c56387d4a7d
Reviewed-on: https://skia-review.googlesource.com/20210
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gm/imagefiltersgraph.cpp b/gm/imagefiltersgraph.cpp
index 3436d69..a369dc0 100644
--- a/gm/imagefiltersgraph.cpp
+++ b/gm/imagefiltersgraph.cpp
@@ -52,8 +52,7 @@
             sk_sp<SkImageFilter> erode(SkErodeImageFilter::Make(4, 4, blur));
             sk_sp<SkImageFilter> color(SkColorFilterImageFilter::Make(std::move(cf),
                                                                       std::move(erode)));
-            sk_sp<SkImageFilter> merge(SkMergeImageFilter::Make(blur, color,
-                                                                SkBlendMode::kSrcOver));
+            sk_sp<SkImageFilter> merge(SkMergeImageFilter::Make(blur, color));
 
             SkPaint paint;
             paint.setImageFilter(std::move(merge));