Add subsetting to SkScaledCodec

src/codec/SkCodec_libgif.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.
  */
 
 #include "SkCodec.h"
 #include "SkColorTable.h"
 #include "SkImageInfo.h"
@@ skipping 112 matching lines @@
     Result prepareToDecode(const SkImageInfo& dstInfo, SkPMColor* inputColorPtr,
             int* inputColorCount, const Options& opts);
 
     /*
      * Initializes the swizzler.
      *
      * @param dstInfo  Output image information.  Dimensions may have been
      *                 adjusted if the image frame size does not match the size
      *                 indicated in the header.
      * @param zeroInit Indicates if destination memory is zero initialized.
+     * @param subsetLeft Left offset for each row decode.
+     * @param subsetWidth Width of each row decode.
      */
-    Result initializeSwizzler(const SkImageInfo& dstInfo, ZeroInitialized zeroInit);
+    Result initializeSwizzler(const SkImageInfo& dstInfo,
+            ZeroInitialized zeroInit, int subsetLeft, int subsetWidth);
 
     SkSampler* getSampler(bool createIfNecessary) override { return fSwizzler; }
 
     /*
      * @return true if the read is successful and false if the read fails.
      */
     bool readRow();
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& opts,
-                   SkPMColor inputColorPtr[], int* inputColorCount) override;
+                   SkPMColor inputColorPtr[], int* inputColorCount, int subsetLeft,
+                   int subsetWidth) override;
 
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;
 
     SkScanlineOrder onGetScanlineOrder() const override;
 
     /*
      * This function cleans up the gif object after the decode completes
      * It is used in a SkAutoTCallIProc template
      */
     static void CloseGif(GifFileType* gif);
@@ skipping 22 matching lines @@
     SkAutoTDeleteArray<uint8_t>             fSrcBuffer;
     const SkIRect                           fFrameRect;
     const uint32_t                          fTransIndex;
     uint32_t                                fFillIndex;
     const bool                              fFrameIsSubset;
     SkAutoTDelete<SkSwizzler>               fSwizzler;
     SkAutoTUnref<SkColorTable>              fColorTable;
 
     typedef SkCodec INHERITED;
 };