Creating a new wrapper for gif decoder

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 "SkImageInfo.h"
+
+#include "gif_lib.h"
+
+/*
+ *
+ * This class implements the decoding for gif images
+ *
+ */
+class SkGifCodec : public SkCodec {
+public:
+
+    /*
+     * Checks the start of the stream to see if the image is a gif
+     */
+    static bool IsGif(SkStream*);
+
+    /*
+     * Assumes IsGif was called and returned true
+     * Creates a gif decoder
+     * Reads enough of the stream to determine the image format
+     */
+    static SkCodec* NewFromStream(SkStream*);
+    
+
+protected:
+
+    /*
+     * Initiates the gif decode
+     */
+    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&,
+            SkPMColor*, int32_t*) override;
+
+    SkEncodedFormat onGetEncodedFormat() const override {
+        return kGIF_SkEncodedFormat;
+    }
+
+private:
+
+    /*
+     * This function cleans up the gif object after the decode completes
+     * It is used in a SkAutoTCallIProc template
+     */
+    static int32_t CloseGif(GifFileType* gif);
+
+    /*
+     * Frees any extension data used in the decode
+     * Used in a SkAutoTCallVProc
+     */
+    static void FreeExtension(SavedImage* image);
+
+    /*
+     * Creates an instance of the decoder
+     * Called only by NewFromStream
+     *
+     * @param srcInfo contains the source width and height
+     * @param stream the stream of image data
+     * @param gif pointer to library type that manages gif decode
+     *            takes ownership
+     */
+    SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream, GifFileType* gif);
+
+    SkAutoTCallIProc<GifFileType, CloseGif> fGif; // owned
+
+    typedef SkCodec INHERITED;
+};