Add 1st cut of FileSystemUsageTracker that tracks the usage changes in FileSystem API.

webkit/fileapi/file_system_usage_tracker.h

+// Copyright (c) 2011 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 WEBKIT_FILEAPI_FILE_SYSTEM_USAGE_TRACKER_H_
+#define WEBKIT_FILEAPI_FILE_SYSTEM_USAGE_TRACKER_H_
+
+#include <deque>
+#include <list>
+#include <map>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/file_path.h"
+#include "base/ref_counted.h"
+#include "webkit/fileapi/file_system_types.h"
+
+class GURL;
+
+namespace base {
+class MessageLoopProxy;
+}
+
+namespace fileapi {
+
+class FileSystemUsageTracker {

[ericu, 2011/02/09 02:05:22]

What's the lifetime of this object?  Is there guaranteed to be exactly one per
profile?  Does it need to be deleted on any particular thread?  What about
requests in progress at destruction time?

[kinuko, 2011/02/09 05:22:36]

Added comments, as I interpreted your questions as so :)
For now it's simply owned by SandboxedFileSystemContext.  I may change this
design a bit if I find it doesn't work.  Any advise is welcome.
(I'll change the comment accordingly if I do so)

[ericu, 2011/02/09 23:03:37]

Great--thanks.

+ public:
+  FileSystemUsageTracker(
+      scoped_refptr<base::MessageLoopProxy> file_message_loop,
+      const FilePath& profile_path,
+      bool is_incognito);
+  ~FileSystemUsageTracker();
+
+  // Get the amount of data stored in the filesystem specified by
+  // |origin_url| and |type|.
+  typedef Callback1<int64 /* usage */>::Type GetUsageCallback;
+  void GetOriginUsage(const GURL& origin_url,
+                      fileapi::FileSystemType type,
+                      GetUsageCallback* callback);
+
+ private:
+  class GetUsageTask;
+  friend class GetUsageTask;

[michaeln, 2011/02/09 00:25:36]

since it's an inner class, do you need the 'friend' keyword here?

[kinuko, 2011/02/09 05:22:36]

Well... I'm not sure if it works in all the compilers we support but some of the
existing classes do so so I figured that it should be ok.
http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#45

+
+  void RegisterUsageTask(GetUsageTask* task);
+  void UnregisterUsageTask(GetUsageTask* task);

[ericu, 2011/02/09 02:05:22]

I'd probably call these [Un]RegisterGetUsageTask, just for consistency.

[kinuko, 2011/02/09 05:22:36]

Agreed, except that the method names reflect the future plan - I'm planning to
have a base class called UsageTask. So I'd like to make them as is for now.

[ericu, 2011/02/09 23:03:37]

OK.

+
+  void DidGetOriginUsage(const std::string& fs_name, int64 usage);
+
+  scoped_refptr<base::MessageLoopProxy> file_message_loop_;
+  FilePath base_path_;
+  bool is_incognito_;
+
+  typedef std::deque<GetUsageTask*> UsageTaskQueue;
+  UsageTaskQueue running_usage_tasks_;
+
+  typedef std::list<GetUsageCallback*> PendingCallbackList;
+  typedef std::map<std::string, PendingCallbackList> PendingUsageCallbackMap;
+  PendingUsageCallbackMap pending_usage_callbacks_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileSystemUsageTracker);
+};
+
+}  // namespace fileapi
+
+#endif  // WEBKIT_FILEAPI_FILE_SYSTEM_USAGE_TRACKER_H_