Create special surfaces according to original device (not always in N32)

src/effects/SkMergeImageFilter.cpp

Index: src/effects/SkMergeImageFilter.cpp
diff --git a/src/effects/SkMergeImageFilter.cpp b/src/effects/SkMergeImageFilter.cpp
index 2dd02ee529ce283b7ecf16a0963b57d106a141ea..42a30a680a7bffa56e3b5c3543c75f6c2c6be18f 100755
--- a/src/effects/SkMergeImageFilter.cpp
+++ b/src/effects/SkMergeImageFilter.cpp
@@ -113,10 +113,7 @@ sk_sp<SkSpecialImage> SkMergeImageFilter::onFilterImage(SkSpecialImage* source,
     const int x0 = bounds.left();
     const int y0 = bounds.top();
 
-    SkImageInfo info = SkImageInfo::MakeN32(bounds.width(), bounds.height(),
-                                            kPremul_SkAlphaType);
-
-    sk_sp<SkSpecialSurface> surf(source->makeSurface(info));
+    sk_sp<SkSpecialSurface> surf(source->makeSurface(bounds));
     if (!surf) {
         return nullptr;
     }