Revert of Split the code for fetching images and for decoding images into two separate classes.

components/image_fetcher/image_decoder.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef COMPONENTS_IMAGE_FETCHER_IMAGE_DECODER_H_
-#define COMPONENTS_IMAGE_FETCHER_IMAGE_DECODER_H_
-
-#include <string>
-#include "base/callback_forward.h"
-
-namespace gfx {
-class Image;
-}  // namespace gfx
-
-namespace image_fetcher {
-
-using ImageDecodedCallback = base::Callback<void(const gfx::Image&)>;
-
-// ImageDecoder defines the common interface for decoding images.
-class ImageDecoder {
- public:
-  ImageDecoder() {}
-  virtual ~ImageDecoder() {}
-
-  // Decodes the passed |image_data| and runs the given callback. The callback
-  // is run even if decoding the image fails. In case an error occured during
-  // decoding the image an empty image is passed to the callback.
-  virtual void DecodeImage(const std::string& image_data,
-                           const ImageDecodedCallback& callback) = 0;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
-};
-
-}  // namespace image_fetcher
-
-#endif  // COMPONENTS_IMAGE_FETCHER_IMAGE_DECODER_H_