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diff --git a/chrome/browser/sync/util/extensions_activity_monitor.h b/chrome/browser/sync/util/extensions_activity_monitor.h
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+++ b/chrome/browser/sync/util/extensions_activity_monitor.h
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+// Copyright (c) 2009 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_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_
+#define CHROME_BROWSER_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_
+
+#include "base/lock.h"
+#include "base/message_loop.h"
+#include "base/ref_counted.h"
+#include "chrome/common/notification_observer.h"
+#include "chrome/common/notification_registrar.h"
+
+namespace browser_sync {
+
+// A class to monitor usage of extensions APIs to send to sync servers, with
+// the ability to purge data once sync servers have acknowledged it (successful
+// commit response).
+//
+// This can be used from any thread (it is a 'monitor' in the synchronization
+// sense as well), HOWEVER
+//
+// *** IT MUST BE DELETED FROM THE UI LOOP ***
+//
+// Consider using MessageLoop::DeleteSoon. (Yes, this means if you allocate
+// an ExtensionsActivityMonitor on a thread other than UI, you must 'new' it).
+class ExtensionsActivityMonitor : public NotificationObserver {
+ public:
+  // A data record of activity performed by extension |extension_id|.
+  struct Record {
+    Record() : bookmark_write_count(0U) {}
+
+    // The human-readable ID identifying the extension responsible
+    // for the activity reported in this Record.
+    std::string extension_id;
+
+    // How many times the extension successfully invoked a write
+    // operation through the bookmarks API since the last CommitMessage.
+    uint32 bookmark_write_count;
+  };
+
+  typedef std::map<std::string, Record> Records;
+
+  // Creates an ExtensionsActivityMonitor to monitor extensions activities on
+  // ChromeThread::UI.
+  ExtensionsActivityMonitor();
+  ~ExtensionsActivityMonitor();
+
+  // Fills |buffer| with snapshot of current records in constant time by
+  // swapping.  This is done mutually exclusively w.r.t methods of this class.
+  void GetAndClearRecords(Records* buffer);
+
+  // Add |records| piece-wise (by extension id) to the set of active records.
+  // This is done mutually exclusively w.r.t the methods of this class.
+  void PutRecords(const Records& records);
+
+  // NotificationObserver implementation.  Called on |ui_loop_|.
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
+ private:
+  Records records_;
+  mutable Lock records_lock_;
+
+  // Used only from UI loop.
+  NotificationRegistrar registrar_;
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_