Add scanline decoding to SkCodec.

src/codec/SkSwizzler.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 SkSwizzler_DEFINED
 #define SkSwizzler_DEFINED
 
 #include "SkCodec.h"
 #include "SkColor.h"
 #include "SkImageInfo.h"
 
 class SkSwizzler : public SkNoncopyable {
 public:
     /**
      *  Enum describing the config of the source data.
      */
     enum SrcConfig {
+        kUnknown,  // Invalid type.
         kGray,
         kIndex1,
         kIndex2,
         kIndex4,
         kIndex,
         kRGB,
         kBGR,
         kRGBX,
         kBGRX,
         kRGBA,
@@ skipping 106 matching lines @@
 
     /**
      *
      * Alternate version of next that allows the caller to specify the row.
      * It is very important to only use one version of next.  Since the other
      * version modifies the dst pointer, it will change the behavior of this
      * function.  We will check this in Debug mode.
      *
      */
     ResultAlpha next(const uint8_t* SK_RESTRICT src, int y);
+
+    /**
+     *  Update the destination row.
+     *
+     *  Typically this is done by next, but for a client that wants to manually
+     *  modify the destination row (for example, for decoding scanline one at a
+     *  time) they can call this before each call to next.
+     *  TODO: Maybe replace this with a version of next which allows supplying the
+     *  destination?
+     */
+    void setDstRow(void* dst) { fDstRow = dst; }
 private:
 
 #ifdef SK_DEBUG
     /*
      *
      * Keep track of which version of next the caller is using
      *
      */
     enum NextMode {
         kUninitialized_NextMode,
@@ skipping 28 matching lines @@
     const SkImageInfo   fDstInfo;
     void*               fDstRow;
     const size_t        fDstRowBytes;
     int                 fCurrY;
 
     SkSwizzler(RowProc proc, const SkPMColor* ctable, int deltaSrc,
                const SkImageInfo& info, void* dst, size_t rowBytes);
 
 };
 #endif // SkSwizzler_DEFINED