chrome: Cleanup class/struct forward declarations

chrome/browser/search/suggestions/image_decoder_impl.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 CHROME_BROWSER_SEARCH_SUGGESTIONS_IMAGE_DECODER_IMPL_H_
 #define CHROME_BROWSER_SEARCH_SUGGESTIONS_IMAGE_DECODER_IMPL_H_
 
 #include <memory>
 #include <vector>
 
 #include "chrome/browser/image_decoder.h"
 #include "components/image_fetcher/image_decoder.h"
 
-class SkBitmap;
-
 namespace suggestions {
 
 // image_fetcher::ImageDecoder Implementation.
 class ImageDecoderImpl : public image_fetcher::ImageDecoder {
  public:
   ImageDecoderImpl();
   ~ImageDecoderImpl() override;
 
   void DecodeImage(
       const std::string& image_data,
       const image_fetcher::ImageDecodedCallback& callback) override;
 
  private:
   class DecodeImageRequest;
 
   // Removes the passed image decode |request| from the internal request queue.
   void RemoveDecodeImageRequest(DecodeImageRequest* request);
 
   // All active image decoding requests.
   std::vector<std::unique_ptr<DecodeImageRequest>> decode_image_requests_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecoderImpl);
 };
 
 }  // namespace suggestions
 
 #endif  // CHROME_BROWSER_SEARCH_SUGGESTIONS_IMAGE_DECODER_IMPL_H_