Add scanline decoding to SkCodec.

src/codec/SkSwizzler.cpp

Index: src/codec/SkSwizzler.cpp
diff --git a/src/codec/SkSwizzler.cpp b/src/codec/SkSwizzler.cpp
index 563933f13a03c16e880c2b8132c7df3657fc4868..8fa3fd4b1bbc1a50edabcbe63ceb972f84978148 100644
--- a/src/codec/SkSwizzler.cpp
+++ b/src/codec/SkSwizzler.cpp
@@ -136,7 +136,7 @@ static bool swizzle_rgba_to_n32_unpremul_skipZ(void* SK_RESTRICT dstRow,
 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) {
@@ -213,6 +213,7 @@ SkSwizzler::SkSwizzler(RowProc proc, const SkPMColor* ctable, int srcBpp,
 
 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++;