Destroy SkScanlineDecoder in the SkCodec subclass destructors

src/codec/SkCodec_libpng.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 "SkCodec_libpng.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 496 matching lines @@
         }
         default:
             SkASSERT(false);
             return false;
     }
 }
 
 SkCodec::Result SkPngCodec::onGetPixels(const SkImageInfo& requestedInfo, void* dst,
                                         size_t rowBytes, const Options& options,
                                         SkPMColor ctable[], int* ctableCount) {
+    // Do not allow a regular decode if the caller has asked for a scanline decoder
+    if (NULL != this->scanlineDecoder()) {
+        SkCodecPrintf("cannot getPixels() if a scanline decoder has been created\n");
+        return kInvalidInput;
+    }
+
     if (!this->handleRewind()) {
         return kCouldNotRewind;
     }
     if (requestedInfo.dimensions() != this->getInfo().dimensions()) {
         return kInvalidScale;
     }
     if (!conversion_possible(requestedInfo, this->getInfo())) {
         return kInvalidConversion;
     }
 
@@ skipping 200 matching lines @@
     bool                fHasAlpha;
     int                 fCurrentRow;
     int                 fHeight;
     size_t              fSrcRowBytes;
     bool                fRewindNeeded;
     SkAutoMalloc        fGarbageRow;
     uint8_t*            fGarbageRowPtr;
     
     
     
-    
 
+
     typedef SkScanlineDecoder INHERITED;
 };
 
 
 SkScanlineDecoder* SkPngCodec::onGetScanlineDecoder(const SkImageInfo& dstInfo,
         const Options& options, SkPMColor ctable[], int* ctableCount) {
     if (!this->handleRewind()) {
         return NULL;
     }
 
@@ skipping 18 matching lines @@
 
     SkASSERT(fNumberPasses != INVALID_NUMBER_PASSES);
     if (fNumberPasses > 1) {
         // interlaced image
         return SkNEW_ARGS(SkPngInterlacedScanlineDecoder, (dstInfo, this));
     }
 
     return SkNEW_ARGS(SkPngScanlineDecoder, (dstInfo, this));
 }