Add scanline decoding to SkCodec.

src/codec/SkSwizzler.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 "SkColorPriv.h"
 #include "SkSwizzler.h"
 #include "SkTemplates.h"
@@ skipping 118 matching lines @@
         src += deltaSrc;
         alphaMask &= alpha;
     }
     return alphaMask != 0xFF;
 }
 */
 
 SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc, const SkPMColor* ctable,
                                        const SkImageInfo& info, void* dst,
                                        size_t dstRowBytes, bool skipZeroes) {
-    if (info.colorType() == kUnknown_SkColorType) {
+    if (info.colorType() == kUnknown_SkColorType || kUnknown == sc) {
         return NULL;
     }
     if (info.minRowBytes() > dstRowBytes) {
         return  NULL;
     }
     if (kIndex == sc && NULL == ctable) {
         return NULL;
     }
     RowProc proc = NULL;
     switch (sc) {
@@ skipping 56 matching lines @@
     , fSrcPixelSize(srcBpp)
     , fDstInfo(info)
     , fDstRow(dst)
     , fDstRowBytes(rowBytes)
     , fCurrY(0)
 {
 }
 
 bool SkSwizzler::next(const uint8_t* SK_RESTRICT src) {
     SkASSERT(fCurrY < fDstInfo.height());
+    SkASSERT(fDstRow != NULL);
     const bool hadAlpha = fRowProc(fDstRow, src, fDstInfo.width(), fSrcPixelSize,
                                    fCurrY, fColorTable);
     fCurrY++;
     fDstRow = SkTAddOffset<void>(fDstRow, fDstRowBytes);
     return hadAlpha;
 }