Split SkBmpCodec into three separate classes

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"
+#include "SkTypes.h"
+
+/*
+ * This class implements the decoding for bmp images using bit masks
+ */
+class SkBmpMaskCodec : public SkBmpCodec {
+public:
+
+    /*
+     * Creates an instance of the decoder
+     *
+     * Called only by SkBmpCodec::NewFromStream
+     * There should be no other callers despite this being public
+     *
+     * @param srcInfo contains the source width and height
+     * @param stream the stream of encoded image data
+     * @param bitsPerPixel the number of bits used to store each pixel
+     * @param masks color masks for certain bmp formats
+     * @param rowOrder indicates whether rows are ordered top-down or bottom-up
+     */
+    SkBmpMaskCodec(const SkImageInfo& srcInfo, SkStream* stream,
+                   uint16_t bitsPerPixel, SkMasks* masks, RowOrder rowOrder);
+
+protected:
+
+    Result onGetPixels(const SkImageInfo& dstInfo, void* dst,
+                       size_t dstRowBytes, const Options&, SkPMColor*,
+                       int*) override;
+
+private:
+
+    bool initializeSwizzler(const SkImageInfo& dstInfo);
+
+    Result decode(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
+                  const Options& opts);
+
+    SkAutoTDelete<SkMasks>              fMasks;        // owned
+    SkAutoTDelete<SkMaskSwizzler>       fMaskSwizzler;
+    SkAutoTDeleteArray<uint8_t>         fSrcBuffer;
+
+    typedef SkBmpCodec INHERITED;
+};