Revert of Revert of replace kIgnore_SkAlphaType with kUnknown_SkAlphaType

src/core/SkImageInfo.cpp

Index: src/core/SkImageInfo.cpp
diff --git a/src/core/SkImageInfo.cpp b/src/core/SkImageInfo.cpp
index 146a3aeed8b0a4a1b04af80f43cb0742e39069db..0e8b0b1292fab1ab702f32a8a1336f1400cec1f5 100644
--- a/src/core/SkImageInfo.cpp
+++ b/src/core/SkImageInfo.cpp
@@ -50,7 +50,7 @@
                                   SkAlphaType* canonical) {
     switch (colorType) {
         case kUnknown_SkColorType:
-            alphaType = kIgnore_SkAlphaType;
+            alphaType = kUnknown_SkAlphaType;
             break;
         case kAlpha_8_SkColorType:
             if (kUnpremul_SkAlphaType == alphaType) {
@@ -61,7 +61,7 @@
         case kARGB_4444_SkColorType:
         case kRGBA_8888_SkColorType:
         case kBGRA_8888_SkColorType:
-            if (kIgnore_SkAlphaType == alphaType) {
+            if (kUnknown_SkAlphaType == alphaType) {
                 return false;
             }
             break;