Add subsetting to SkScaledCodec

include/codec/SkScaledCodec.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 SkScaledCodec_DEFINED
 #define SkScaledCodec_DEFINED
 
 #include "SkCodec.h"
 
 class SkStream;
 
 /**
  * This class implements scaling, by sampling scanlines in the y direction.
  * x-wise sampling is implemented in the swizzler, when getScanlines() is called.
  */
 class SkScaledCodec : public SkCodec {
 public:
     static SkCodec* NewFromStream(SkStream*);
     static SkCodec* NewFromData(SkData*);
 
     virtual ~SkScaledCodec();
 
-    static void ComputeSampleSize(const SkISize& dstDim, const SkISize& srcDim,
+    static void ComputeSampleSize(const SkISize& dstSize, const SkISize& srcSize,
                                   int* sampleSizeX, int* sampleSizeY);
 
 protected:
     bool onRewind() override;
 
     /**
      * Recommend a set of destination dimensions given a requested scale
      */
     SkISize onGetScaledDimensions(float desiredScale) const override;
     bool onDimensionsSupported(const SkISize&) override;
 
+    bool onGetScaledSubsetDimensions(float desiredScale, Options* options) const override;
+
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override {
         return fCodec->getEncodedFormat();
     }
 
     bool onReallyHasAlpha() const override {
         return fCodec->reallyHasAlpha();
     }
 
     uint32_t onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const override;
 
     SkScanlineOrder onGetScanlineOrder() const override;
 
 private:
 
+    Result nativeDecode(const SkImageInfo& scaledInfo, void* dst, size_t rowBytes,
+            const SkIRect& scaledSubsetRect, ZeroInitialized zeroInit, int* rowsDecoded);
+
+    Result sampledDecode(const SkImageInfo& decodeInfo, void* dst, size_t rowBytes,
+            const SkIRect& subsetRect, const SkIRect& scaledSubsetRect, int sampleX, int sampleY,
+            ZeroInitialized zeroInit, int* rowsDecoded);
+
     SkAutoTDelete<SkCodec> fCodec;
 
     explicit SkScaledCodec(SkCodec*);
 
     typedef SkCodec INHERITED;
 };
 #endif // SkScaledCodec_DEFINED