Revert of Add SkCodec, including PNG implementation.

src/codec/SkCodec_libpng.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"
-
-extern "C" {
-    // FIXME: I'd like to force all platforms to use the same decoder, but this
-    // means an extra dependency on Mac/Win.
-    #include "png.h"
-}
-
-class SkStream;
-
-class SkPngCodec : public SkCodec {
-public:
-    // Assumes IsPng was called and returned true.
-    static SkCodec* NewFromStream(SkStream*);
-    static bool IsPng(SkStream*);
-protected:
-    Result onGetPixels(const SkImageInfo&, void*, size_t, SkPMColor*, int*) SK_OVERRIDE;
-private:
-    png_structp             fPng_ptr;
-    png_infop               fInfo_ptr;
-
-    SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop);
-    ~SkPngCodec();
-
-    typedef SkCodec INHERITED;
-};