Supervised user blacklist: Add downloader class to download a blacklist if needed.

chrome/browser/supervised_user/experimental/supervised_user_blacklist_downloader.h

+// Copyright 2014 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_SUPERVISED_USER_EXPERIMENTAL_SUPERVISED_USER_BLACKLIST_DOWNLOADER_H_
+#define CHROME_BROWSER_SUPERVISED_USER_EXPERIMENTAL_SUPERVISED_USER_BLACKLIST_DOWNLOADER_H_
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "net/url_request/url_fetcher_delegate.h"
+
+namespace base {
+class FilePath;
+}  // namespace base
+
+namespace net {
+class URLFetcher;
+class URLRequestContextGetter;
+}  // namespace net
+
+class GURL;
+
+// Helper class to download a blacklist file from a given URL and store it in a
+// local file. If the local file already exists, reports success without
+// downloading anything.
+class SupervisedUserBlacklistDownloader : public net::URLFetcherDelegate {
+ public:
+  typedef base::Callback<void(bool /* success */)> DownloadFinishedCallback;
+
+  // Directly starts the download (if necessary) and runs |callback| when done.
+  // If the instance is destroyed before it is finished, |callback| is not run.
+  SupervisedUserBlacklistDownloader(
+      const GURL& url,
+      const base::FilePath& path,
+      net::URLRequestContextGetter* request_context,
+      const DownloadFinishedCallback& callback);
+  virtual ~SupervisedUserBlacklistDownloader();
+
+ private:
+  // net::URLFetcherDelegate implementation.
+  virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE;
+
+  void OnFileExistsCheckDone(bool exists);
+
+  DownloadFinishedCallback callback_;
+
+  scoped_ptr<net::URLFetcher> fetcher_;
+
+  base::WeakPtrFactory<SupervisedUserBlacklistDownloader> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SupervisedUserBlacklistDownloader);
+};
+
+#endif  // CHROME_BROWSER_SUPERVISED_USER_EXPERIMENTAL_SUPERVISED_USER_BLACKLIST_DOWNLOADER_H_