Make SkPngCodec decode progressively.

src/android/SkBitmapRegionDecoder.cpp

Index: src/android/SkBitmapRegionDecoder.cpp
diff --git a/src/android/SkBitmapRegionDecoder.cpp b/src/android/SkBitmapRegionDecoder.cpp
index 101efbda452c49a2e4b9c695246b806ff56025e5..d7d26809c541eba9cdf44e43e58c32271bc5c2fb 100644
--- a/src/android/SkBitmapRegionDecoder.cpp
+++ b/src/android/SkBitmapRegionDecoder.cpp
@@ -41,10 +41,9 @@ SkBitmapRegionDecoder* SkBitmapRegionDecoder::Create(
             }
 
             // If the image is a jpeg or a png, the scanline ordering should always be
-            // kTopDown or kNone.  It is relevant to check because this implementation
-            // only supports these two scanline orderings.
-            SkASSERT(SkCodec::kTopDown_SkScanlineOrder == codec->getScanlineOrder() ||
-                    SkCodec::kNone_SkScanlineOrder == codec->getScanlineOrder());
+            // kTopDown.  It is relevant to check because this implementation only
+            // supports this scanline ordering.
+            SkASSERT(SkCodec::kTopDown_SkScanlineOrder == codec->getScanlineOrder());
 
             return new SkBitmapRegionCanvas(codec.release());
         }