Add alphaType() to SkImage

src/pdf/SkPDFBitmap.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorPriv.h"
 #include "SkData.h"
 #include "SkDeflate.h"
@@ skipping 14 matching lines @@
         // We must check to see if the bitmap has a color table.
         SkAutoLockPixels autoLockPixels(*dst);
         if (!dst->getColorTable()) {
             // We can't use an indexed bitmap with no colortable.
             dst->reset();
         } else {
             return;
         }
     }
     // no pixels or wrong size: fill with zeros.
-    SkAlphaType at = image->isOpaque() ? kOpaque_SkAlphaType : kPremul_SkAlphaType;
-    dst->setInfo(SkImageInfo::MakeN32(image->width(), image->height(), at));
+    dst->setInfo(SkImageInfo::MakeN32(image->width(), image->height(), image->alphaType()));
 }
 
 bool image_compute_is_opaque(const SkImage* image) {
     if (image->isOpaque()) {
         return true;
     }
     // keep output PDF small at cost of possible resource use.
     SkBitmap bm;
     image_get_ro_pixels(image, &bm);
     return SkBitmap::ComputeIsOpaque(bm);
@@ skipping 481 matching lines @@
 
     sk_sp<SkPDFObject> smask;
     if (!image_compute_is_opaque(image.get())) {
         smask = sk_make_sp<PDFAlphaBitmap>(image);
     }
     #ifdef SK_PDF_IMAGE_STATS
     gRegularImageObjects.fetch_add(1);
     #endif
     return sk_make_sp<PDFDefaultBitmap>(std::move(image), std::move(smask));
 }