Add alphaType() to SkImage

src/pdf/SkPDFBitmap.cpp

Index: src/pdf/SkPDFBitmap.cpp
diff --git a/src/pdf/SkPDFBitmap.cpp b/src/pdf/SkPDFBitmap.cpp
index 887bca4ab0f427b5e845e821d64f19099ca59ec6..772745ca50aa29e05fc4435e04a556746fc841d2 100644
--- a/src/pdf/SkPDFBitmap.cpp
+++ b/src/pdf/SkPDFBitmap.cpp
@@ -32,8 +32,7 @@ void image_get_ro_pixels(const SkImage* image, SkBitmap* dst) {
         }
     }
     // 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) {