Add the download component and initial setup

components/download/internal/background_download_service_impl.h

Index: components/download/internal/background_download_service_impl.h
diff --git a/components/download/internal/background_download_service_impl.h b/components/download/internal/background_download_service_impl.h
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index 0000000000000000000000000000000000000000..b87f41fc7be79436d92c4ff89d898d5fee155085
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+++ b/components/download/internal/background_download_service_impl.h
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+// Copyright 2017 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_DOWNLOAD_INTERNAL_BACKGROUND_DOWNLOAD_SERVICE_IMPL_H_
+#define COMPONENTS_DOWNLOAD_INTERNAL_BACKGROUND_DOWNLOAD_SERVICE_IMPL_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "components/download/public/background_download_service.h"
+
+namespace download {
+
+struct DownloadParams;
+struct SchedulingParams;
+
+// The internal implementation of the BackgroundDownloadService.
+class BackgroundDownloadServiceImpl : public BackgroundDownloadService {
+ public:
+  BackgroundDownloadServiceImpl();
+  ~BackgroundDownloadServiceImpl() override;
+
+  // BackgroundDownloadService implementation.
+  void StartDownload(const DownloadParams& download_params) override;
+  void PauseDownload(const std::string& guid) override;
+  void ResumeDownload(const std::string& guid) override;
+  void CancelDownload(const std::string& guid) override;
+  void ChangeDownloadCriteria(const std::string& guid,
+                              const SchedulingParams& params) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BackgroundDownloadServiceImpl);
+};
+
+}  // namespace download
+
+#endif  // COMPONENTS_DOWNLOAD_INTERNAL_BACKGROUND_DOWNLOAD_SERVICE_IMPL_H_