Revert of Revert of replace kIgnore_SkAlphaType with kUnknown_SkAlphaType

src/core/SkImageInfo.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageInfo.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
@@ skipping 32 matching lines @@
     SkASSERT(0 == (fAlphaType & ~0xFF));
     SkASSERT(0 == (fColorType & ~0xFF));
     uint32_t packed = (fProfileType << 16) | (fAlphaType << 8) | fColorType;
     buffer.write32(packed);
 }
 
 bool SkColorTypeValidateAlphaType(SkColorType colorType, SkAlphaType alphaType,
                                   SkAlphaType* canonical) {
     switch (colorType) {
         case kUnknown_SkColorType:
-            alphaType = kIgnore_SkAlphaType;
+            alphaType = kUnknown_SkAlphaType;
             break;
         case kAlpha_8_SkColorType:
             if (kUnpremul_SkAlphaType == alphaType) {
                 alphaType = kPremul_SkAlphaType;
             }
             // fall-through
         case kIndex_8_SkColorType:
         case kARGB_4444_SkColorType:
         case kRGBA_8888_SkColorType:
         case kBGRA_8888_SkColorType:
-            if (kIgnore_SkAlphaType == alphaType) {
+            if (kUnknown_SkAlphaType == alphaType) {
                 return false;
             }
             break;
         case kRGB_565_SkColorType:
             alphaType = kOpaque_SkAlphaType;
             break;
         default:
             return false;
     }
     if (canonical) {
@@ skipping 38 matching lines @@
     // here x,y are either 0 or negative
     fPixels = ((char*)fPixels - y * fRowBytes - x * fInfo.bytesPerPixel());
     // the intersect may have shrunk info's logical size
     fInfo = fInfo.makeWH(srcR.width(), srcR.height());
     fX = srcR.x();
     fY = srcR.y();
 
     return true;
 }