Move all knowledge of X sampling into SkScaledCodec

src/codec/SkBmpMaskCodec.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 "SkBmpCodec.h"
 #include "SkImageInfo.h"
 #include "SkMaskSwizzler.h"
@@ skipping 27 matching lines @@
                        size_t dstRowBytes, const Options&, SkPMColor*,
                        int*) override;
 
     SkCodec::Result prepareToDecode(const SkImageInfo& dstInfo,
             const SkCodec::Options& options, SkPMColor inputColorPtr[],
             int* inputColorCount) override;
 
 private:
 
     bool initializeSwizzler(const SkImageInfo& dstInfo);
+    SkSampler* getSampler() override { return fMaskSwizzler; }
 
     Result decodeRows(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
                       const Options& opts) override;
 
     SkAutoTDelete<SkMasks>              fMasks;        // owned
     SkAutoTDelete<SkMaskSwizzler>       fMaskSwizzler;
     const size_t                        fSrcRowBytes;
     SkAutoTDeleteArray<uint8_t>         fSrcBuffer;
 
     typedef SkBmpCodec INHERITED;
 };