replace kIgnore_SkAlphaType with kUnknown_SkAlphaType

src/core/SkConfig8888.cpp

Index: src/core/SkConfig8888.cpp
diff --git a/src/core/SkConfig8888.cpp b/src/core/SkConfig8888.cpp
index 8b47a20633fa67bb95fdc6416f2f44faa9524160..85e208f2875b987edc253a925f75b7d46ea5f81d 100644
--- a/src/core/SkConfig8888.cpp
+++ b/src/core/SkConfig8888.cpp
@@ -54,8 +54,8 @@ static bool is_32bit_colortype(SkColorType ct) {
 }
 
 static AlphaVerb compute_AlphaVerb(SkAlphaType src, SkAlphaType dst) {
-    SkASSERT(kIgnore_SkAlphaType != src);
-    SkASSERT(kIgnore_SkAlphaType != dst);
+    SkASSERT(kUnknown_SkAlphaType != src);
+    SkASSERT(kUnknown_SkAlphaType != dst);
 
     if (kOpaque_SkAlphaType == src || kOpaque_SkAlphaType == dst || src == dst) {
         return kNothing_AlphaVerb;