Allow creating multiple scanline decoders.

include/codec/SkScanlineDecoder.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkScanlineDecoder_DEFINED
 #define SkScanlineDecoder_DEFINED
 
 #include "SkTypes.h"
 #include "SkCodec.h"
 #include "SkTemplates.h"
 #include "SkImageInfo.h"
 
 class SkScanlineDecoder : public SkNoncopyable {
 public:
     /**
      *  Clean up after reading/skipping scanlines.
      *
      *  It is possible that not all scanlines will have been read/skipped.  In
      *  fact, in the case of subset decodes, it is likely that there will be
      *  scanlines at the bottom of the image that have been ignored.
-     *
-     *  Note for implementations: An SkScanlineDecoder will be deleted by (and
-     *  therefore *before*) its associated SkCodec, in case the order matters.
-     *  However, while the SkCodec base class maintains ownership of the
-     *  SkScanlineDecoder, the subclass will be deleted before the scanline
-     *  decoder.  If this is an issue, detachScanlineDecoder() provides
-     *  a means for the subclass to take ownership of the SkScanlineDecoder.
      */
     virtual ~SkScanlineDecoder() {}
 
     /**
      *  Write the next countLines scanlines into dst.
      *
      *  @param dst Must be non-null, and large enough to hold countLines
      *      scanlines of size rowBytes.
      *  @param countLines Number of lines to write.
      *  @param rowBytes Number of bytes per row. Must be large enough to hold
@@ skipping 63 matching lines @@
         // Calling the virtual method also means we do not double count
         // countLines.
         return this->onGetScanlines(storage.get(), countLines, 0);
     }
 
     virtual SkCodec::Result onGetScanlines(void* dst, int countLines,
                                                     size_t rowBytes) = 0;
 
 };
 #endif // SkScanlineDecoder_DEFINED