Make SkPngCodec decode progressively.

src/android/SkBitmapRegionDecoder.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 "SkBitmapRegionCanvas.h"
 #include "SkBitmapRegionCodec.h"
 #include "SkBitmapRegionDecoder.h"
@@ skipping 23 matching lines @@
                 case SkEncodedFormat::kJPEG_SkEncodedFormat:
                 case SkEncodedFormat::kPNG_SkEncodedFormat:
                     break;
                 default:
                     // FIXME: Support webp using a special case.  Webp does not support
                     //        scanline decoding.
                     return nullptr;
             }
 
             // 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());
         }
         case kAndroidCodec_Strategy: {
             SkAutoTDelete<SkAndroidCodec> codec =
                     SkAndroidCodec::NewFromStream(streamDeleter.release());
             if (nullptr == codec) {
                 SkCodecPrintf("Error: Failed to create codec.\n");
                 return NULL;
             }
 
             SkEncodedFormat format = codec->getEncodedFormat();
             switch (format) {
                 case SkEncodedFormat::kJPEG_SkEncodedFormat:
                 case SkEncodedFormat::kPNG_SkEncodedFormat:
                 case SkEncodedFormat::kWEBP_SkEncodedFormat:
                     break;
                 default:
                     return nullptr;
             }
 
             return new SkBitmapRegionCodec(codec.release());
         }
         default:
             SkASSERT(false);
             return nullptr;
     }
 }