Revert of replace kIgnore_SkAlphaType with kUnknown_SkAlphaType

include/core/SkImageInfo.h

Index: include/core/SkImageInfo.h
diff --git a/include/core/SkImageInfo.h b/include/core/SkImageInfo.h
index d915c09255f345abe86d419153ba96c7a52360a2..f928416fe7bd1c9df84ef431ee13229f35c184d1 100644
--- a/include/core/SkImageInfo.h
+++ b/include/core/SkImageInfo.h
@@ -19,7 +19,12 @@
  *  Describes how to interpret the alpha compoent of a pixel.
  */
 enum SkAlphaType {
-    kUnknown_SkAlphaType,
+    /**
+     *  All pixels should be treated as opaque, regardless of the value stored
+     *  in their alpha field. Used for legacy images that wrote 0 or garbarge
+     *  in their alpha field, but intended the RGB to be treated as opaque.
+     */
+    kIgnore_SkAlphaType,
 
     /**
      *  All pixels are stored as opaque. This differs slightly from kIgnore in
@@ -48,7 +53,11 @@
 };
 
 static inline bool SkAlphaTypeIsOpaque(SkAlphaType at) {
-    return kOpaque_SkAlphaType == at;
+    SK_COMPILE_ASSERT(kIgnore_SkAlphaType < kOpaque_SkAlphaType, bad_alphatype_order);
+    SK_COMPILE_ASSERT(kPremul_SkAlphaType > kOpaque_SkAlphaType, bad_alphatype_order);
+    SK_COMPILE_ASSERT(kUnpremul_SkAlphaType > kOpaque_SkAlphaType, bad_alphatype_order);
+
+    return (unsigned)at <= kOpaque_SkAlphaType;
 }
 
 static inline bool SkAlphaTypeIsValid(unsigned value) {
@@ -152,7 +161,7 @@
         : fWidth(0)
         , fHeight(0)
         , fColorType(kUnknown_SkColorType)
-        , fAlphaType(kUnknown_SkAlphaType)
+        , fAlphaType(kIgnore_SkAlphaType)
         , fProfileType(kLinear_SkColorProfileType)
     {}
 
@@ -191,7 +200,7 @@
     }
 
     static SkImageInfo MakeUnknown(int width, int height) {
-        return SkImageInfo(width, height, kUnknown_SkColorType, kUnknown_SkAlphaType,
+        return SkImageInfo(width, height, kUnknown_SkColorType, kIgnore_SkAlphaType,
                            kLinear_SkColorProfileType);
     }