C++ Readability Review for thestig.

content/browser/media_device_notifications_linux.h

 // Copyright (c) 2012 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.
 
+// MediaDeviceNotificationsLinux listens for mount point changes and notifies
+// the SystemMonitor about the addition and deletion of media devices.
+
 #ifndef CONTENT_BROWSER_MEDIA_DEVICE_NOTIFICATIONS_LINUX_H_
 #define CONTENT_BROWSER_MEDIA_DEVICE_NOTIFICATIONS_LINUX_H_
 #pragma once
 
 #include <map>
 #include <set>
 #include <string>
 #include <utility>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
-#include "base/file_path.h"
 #include "base/files/file_path_watcher.h"
 #include "base/memory/ref_counted.h"
 #include "base/system_monitor/system_monitor.h"
 #include "content/common/content_export.h"
 
+class FilePath;
+
 namespace content {
 
 class CONTENT_EXPORT MediaDeviceNotificationsLinux
     : public base::RefCountedThreadSafe<MediaDeviceNotificationsLinux> {
  public:
   explicit MediaDeviceNotificationsLinux(const FilePath& path);
 
   // Must be called for MediaDeviceNotificationsLinux to work.
   void Init();
 
  protected:
+  friend class base::RefCountedThreadSafe<MediaDeviceNotificationsLinux>;
+
+  // Avoids code deleting the object while there are references to it.

[ajl, 2012/04/03 23:35:57]

I think it would be better in this to explicitly mention how this prevents
deletion except by the reference counted pointer class, i.e. explain *how*
making the destructor protected avoids deleting the objects while references
exist.  Otherwise the connection isn't clear.

[Lei Zhang, 2012/04/04 05:31:29]

Done.

   virtual ~MediaDeviceNotificationsLinux();
 
   virtual void OnFilePathChanged(const FilePath& path);
 
  private:
-  friend class base::RefCountedThreadSafe<MediaDeviceNotificationsLinux>;
+  class WatcherDelegate;
 
-  typedef std::string MountDevice;
-  typedef std::string MountPoint;
-  typedef std::pair<MountDevice,
+  // (mount device, device id)
+  typedef std::pair<std::string,
                     base::SystemMonitor::DeviceIdType> MountDeviceAndId;
-  typedef std::map<MountPoint, MountDeviceAndId> MountMap;
-
-  // A simple pass-through class. MediaDeviceNotificationsLinux cannot directly
-  // inherit from FilePathWatcher::Delegate due to multiple inheritance.
-  class WatcherDelegate : public base::files::FilePathWatcher::Delegate {
-   public:
-    explicit WatcherDelegate(MediaDeviceNotificationsLinux* notifier);
-
-    // base::files::FilePathWatcher::Delegate implementation.
-    virtual void OnFilePathChanged(const FilePath& path) OVERRIDE;
-
-   private:
-    friend class base::RefCountedThreadSafe<WatcherDelegate>;
-
-    virtual ~WatcherDelegate();
-    MediaDeviceNotificationsLinux* notifier_;
-
-    DISALLOW_COPY_AND_ASSIGN(WatcherDelegate);
-  };
+  // Mapping of mount points to MountDeviceAndId.
+  typedef std::map<std::string, MountDeviceAndId> MountMap;
 
   void InitOnFileThread();
 
   // Parse the mtab file and find all changes.
   void UpdateMtab();
 
   // Read the mtab file entries into |mtab|.
   void ReadMtab(MountMap* mtab);
 
   // For a new device mounted at |mount_point|, see if it is a media device by
   // checking for the existence of a DCIM directory.
   // If it is a media device, return true, otherwise return false.
   // Mac OS X behaves similarly, but this is not the only heuristic it uses.
   // TODO(vandebo) Try to figure out how Mac OS X decides this.
-  bool IsMediaDevice(const MountPoint& mount_point);
+  bool IsMediaDevice(const std::string& mount_point);
 
   // Add a media device with a given device and mount device. Assign it a device
   // id as well.
-  void AddNewDevice(const MountDevice& mount_device,
-                    const MountPoint& mount_point,
+  void AddNewDevice(const std::string& mount_device,
+                    const std::string& mount_point,
                     base::SystemMonitor::DeviceIdType* device_id);
 
   // Remove a media device with a given device id.
   void RemoveOldDevice(const base::SystemMonitor::DeviceIdType& device_id);
 
   // Whether Init() has been called or not.
   bool initialized_;
 
   // Mtab file that lists the mount points.
   const FilePath mtab_path_;
@@ skipping 12 matching lines @@
 
   // Set of known file systems that we care about.
   std::set<std::string> known_file_systems_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaDeviceNotificationsLinux);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_DEVICE_NOTIFICATIONS_LINUX_H_