Reland kPMColor_SkColorType to kN32_SkColorType.

src/effects/SkAlphaThresholdFilter.cpp

Index: src/effects/SkAlphaThresholdFilter.cpp
diff --git a/src/effects/SkAlphaThresholdFilter.cpp b/src/effects/SkAlphaThresholdFilter.cpp
index f938ba61bbe738a2bf6f5a72fd45fe7b75a80cfe..205e9a9516058f946279ea35b486b352f0bcd7e5 100644
--- a/src/effects/SkAlphaThresholdFilter.cpp
+++ b/src/effects/SkAlphaThresholdFilter.cpp
@@ -306,9 +306,9 @@ void SkAlphaThresholdFilterImpl::flatten(SkWriteBuffer& buffer) const {
 bool SkAlphaThresholdFilterImpl::onFilterImage(Proxy*, const SkBitmap& src,
                                                const Context& ctx, SkBitmap* dst,
                                                SkIPoint* offset) const {
-    SkASSERT(src.colorType() == kPMColor_SkColorType);
+    SkASSERT(src.colorType() == kN32_SkColorType);
 
-    if (src.colorType() != kPMColor_SkColorType) {
+    if (src.colorType() != kN32_SkColorType) {
         return false;
     }