Revert AlphaThresholdFilter to its old behavior wrt premul

TBR=borenet@google.com

This fixes the "serialize-8888 gm  imagealphathreshold_surface" failure related to:
https://codereview.chromium.org/1879643003/ (Switch AlphaThresholdFilter over to new onFilterImage interface)

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1885633003

Review URL: https://codereview.chromium.org/1885633003

diff --git a/src/effects/SkAlphaThresholdFilter.cpp b/src/effects/SkAlphaThresholdFilter.cpp
index 832fcb3..a548430 100644 (file)
--- a/src/effects/SkAlphaThresholdFilter.cpp
+++ b/src/effects/SkAlphaThresholdFilter.cpp
@@ -412,7 +412,7 @@ sk_sp<SkSpecialImage> SkAlphaThresholdFilterImpl::onFilterImage(SkSpecialImage*
     }
 
     SkImageInfo info = SkImageInfo::MakeN32(bounds.width(), bounds.height(),
-                                            inputBM.alphaType());
+                                            kPremul_SkAlphaType);
 
     SkBitmap dst;
     if (!dst.tryAllocPixels(info)) {