unify peekPixels around pixmap parameter

src/core/SkSpecialImage.cpp

Index: src/core/SkSpecialImage.cpp
diff --git a/src/core/SkSpecialImage.cpp b/src/core/SkSpecialImage.cpp
index f5f88329c4a3bf86e5f21b252279ffdb53108918..a55fe650293e0216b8ddc4167e4864fdcfb7f55a 100644
--- a/src/core/SkSpecialImage.cpp
+++ b/src/core/SkSpecialImage.cpp
@@ -114,11 +114,9 @@ public:
         } else
 #endif
         {
-            SkImageInfo info;
-            size_t rowBytes;
-
-            if (fImage->peekPixels(&info, &rowBytes)) {
-                return info.height() * rowBytes;
+            SkPixmap pm;
+            if (fImage->peekPixels(&pm)) {
+                return pm.height() * pm.rowBytes();
             }
         }
         return 0;