Componentize component_updater: Replace content::BrowserThread usage with task runners

chrome/browser/component_updater/crx_downloader.h

 // Copyright 2013 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_COMPONENT_UPDATER_CRX_DOWNLOADER_H_
 #define CHROME_BROWSER_COMPONENT_UPDATER_CRX_DOWNLOADER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/sequenced_task_runner.h"
+#include "base/threading/thread_checker.h"
 #include "url/gurl.h"
 
+namespace base {
+class SequencedTaskRunner;
+class SingleThreadTaskRunner;
+}
+
 namespace net {
 class URLRequestContextGetter;
 }
 
 namespace component_updater {
 
 // Defines a download interface for downloading components, with retrying on
 // fallback urls in case of errors. This class implements a chain of
 // responsibility design pattern. It can give successors in the chain a chance
 // to handle a download request, until one of them succeeds, or there are no
 // more urls or successors to try. A callback is always called at the end of
 // the download, one time only.
 // When multiple urls and downloaders exists, first all the urls are tried, in
 // the order they are provided in the StartDownload function argument. After
 // that, the download request is routed to the next downloader in the chain.
-// The members of this class expect to be called from the UI thread only.
+// The members of this class expect to be called from the main thread only.
 class CrxDownloader {
  public:
   struct DownloadMetrics {
     enum Downloader { kNone = 0, kUrlFetcher, kBits };
 
     DownloadMetrics();
 
     GURL url;
 
     Downloader downloader;
@@ skipping 32 matching lines @@
   typedef base::Callback<void(const Result& result)> DownloadCallback;
 
   // The callback may fire 0 or many times during a download. Since this
   // class implements a chain of responsibility, the callback can fire for
   // different urls and different downloaders. The number of actual downloaded
   // bytes is not guaranteed to monotonically increment over time.
   typedef base::Callback<void(const Result& result)> ProgressCallback;
 
   // Factory method to create an instance of this class and build the
   // chain of responsibility. |is_background_download| specifies that a
   // background downloader be used, if the platform supports it.

[blundell, 2014/07/15 08:45:20]

The new params should be documented.

[tommycli, 2014/07/15 18:58:25]

Done.

   static CrxDownloader* Create(
       bool is_background_download,
       net::URLRequestContextGetter* context_getter,
-      scoped_refptr<base::SequencedTaskRunner> task_runner);
+      scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner,

[blundell, 2014/07/15 08:45:20]

It would be good if these params could be given names that reflect their
intended usage.

[tommycli, 2014/07/15 18:58:25]

Done.

+      scoped_refptr<base::SingleThreadTaskRunner> single_thread_task_runner);
   virtual ~CrxDownloader();
 
   void set_progress_callback(const ProgressCallback& progress_callback);
 
   // Starts the download. One instance of the class handles one download only.
   // One instance of CrxDownloader can only be started once, otherwise the
   // behavior is undefined. The callback gets invoked if the download can't
   // be started.
   void StartDownloadFromUrl(const GURL& url,
                             const DownloadCallback& download_callback);
@@ skipping 19 matching lines @@
 
   // Calls the callback when progress is made.
   void OnDownloadProgress(const Result& result);
 
   // Returns the url which is currently being downloaded from.
   GURL url() const;
 
  private:
   virtual void DoStartDownload(const GURL& url) = 0;
 
+  base::ThreadChecker thread_checker_;
+
   std::vector<GURL> urls_;
   scoped_ptr<CrxDownloader> successor_;
   DownloadCallback download_callback_;
   ProgressCallback progress_callback_;
 
   std::vector<GURL>::iterator current_url_;
 
   std::vector<DownloadMetrics> download_metrics_;
 
   DISALLOW_COPY_AND_ASSIGN(CrxDownloader);
 };
 
 }  // namespace component_updater
 
 #endif  // CHROME_BROWSER_COMPONENT_UPDATER_CRX_DOWNLOADER_H_