store SkAlphaType inside SkBitmap, on road to support unpremul

src/images/SkImageDecoder.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkImageDecoder.h"
 #include "SkBitmap.h"
@@ skipping 227 matching lines @@
         // savings are more important than speed here. This also means
         // that the pixels in dst can not be reused (though there is no
         // allocation, which was already done on src).
         int x = (dstX - srcX) / sampleSize;
         int y = (dstY - srcY) / sampleSize;
         SkIRect subset = SkIRect::MakeXYWH(x, y, w, h);
         return src->extractSubset(dst, subset);
     }
     // if the destination has no pixels then we must allocate them.
     if (dst->isNull()) {
-        dst->setConfig(src->getConfig(), w, h);
-        dst->setIsOpaque(src->isOpaque());
+        dst->setConfig(src->getConfig(), w, h, 0, src->alphaType());
 
         if (!this->allocPixelRef(dst, NULL)) {
             SkDEBUGF(("failed to allocate pixels needed to crop the bitmap"));
             return false;
         }
     }
     // check to see if the destination is large enough to decode the desired
     // region. If this assert fails we will just draw as much of the source
     // into the destination that we can.
     if (dst->width() < w || dst->height() < h) {
@@ skipping 204 matching lines @@
             if (kUnknown_Format == *format) {
                 if (stream->rewind()) {
                     *format = GetStreamFormat(stream);
                 }
             }
         }
         delete codec;
     }
     return success;
 }