store SkAlphaType inside SkBitmap, on road to support unpremul

src/ports/SkImageDecoder_CG.cpp

 /*
  * Copyright 2008 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 "SkCGUtils.h"
 #include "SkColorPriv.h"
 #include "SkImageDecoder.h"
@@ skipping 86 matching lines @@
 
     CGContextDrawImage(cg, CGRectMake(0, 0, width, height), image);
     CGContextRelease(cg);
 
     CGImageAlphaInfo info = CGImageGetAlphaInfo(image);
     switch (info) {
         case kCGImageAlphaNone:
         case kCGImageAlphaNoneSkipLast:
         case kCGImageAlphaNoneSkipFirst:
             SkASSERT(SkBitmap::ComputeIsOpaque(*bm));
-            bm->setIsOpaque(true);
+            bm->setAlphaType(kOpaque_SkAlphaType);
             break;
         default:
             // we don't know if we're opaque or not, so compute it.
-            bm->computeAndSetOpaquePredicate();
+            if (SkBitmap::ComputeIsOpaque(*bm)) {
+                bm->setAlphaType(kOpaque_SkAlphaType);
+            }
     }
     if (!bm->isOpaque() && this->getRequireUnpremultipliedColors()) {
         // CGBitmapContext does not support unpremultiplied, so the image has been premultiplied.
         // Convert to unpremultiplied.
         for (int i = 0; i < width; ++i) {
             for (int j = 0; j < height; ++j) {
                 uint32_t* addr = bm->getAddr32(i, j);
                 *addr = unpremultiply_pmcolor(*addr);
             }
         }
+        bm->setAlphaType(kUnpremul_SkAlphaType);
     }
     bm->unlockPixels();
     return true;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 extern SkImageDecoder* image_decoder_from_stream(SkStreamRewindable*);
 
 SkImageDecoder* SkImageDecoder::Factory(SkStreamRewindable* stream) {
@@ skipping 162 matching lines @@
 
     SkAutoTCallVProc<const void, CFRelease> arsrc(imageSrc);
     const CFStringRef name = CGImageSourceGetType(imageSrc);
     if (NULL == name) {
         return SkImageDecoder::kUnknown_Format;
     }
     return UTType_to_Format(name);
 }
 
 static SkImageDecoder_FormatReg gFormatReg(get_format_cg);