[Sync] Fix use of ObserverList by multiple threads.

chrome/browser/sync/syncable/syncable.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 CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_H_
 #define CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_H_
 #pragma once
 
 #include <algorithm>
 #include <bitset>
@@ skipping 978 matching lines @@
 
   struct Kernel {
     Kernel(const FilePath& db_path, const std::string& name,
            const KernelLoadInfo& info);
 
     ~Kernel();
 
     void AddRef();  // For convenience.
     void Release();
 
+    void AddChangeListener(DirectoryChangeListener* listener);
+    void RemoveChangeListener(DirectoryChangeListener* listener);
+
+    void CopyChangeListeners(
+        ObserverList<DirectoryChangeListener>* change_listeners);
+
     FilePath const db_path;
     // TODO(timsteele): audit use of the member and remove if possible
     volatile base::subtle::AtomicWord refcount;
 
     // Implements ReadTransaction / WriteTransaction using a simple lock.
     base::Lock transaction_mutex;
 
     // The name of this directory.
     std::string const name;
 
@@ skipping 22 matching lines @@
     // necessarily).  Dirtyness is confirmed in TakeSnapshotForSaveChanges().
     MetahandleSet* const dirty_metahandles;
 
     // When a purge takes place, we remove items from all our indices and stash
     // them in here so that SaveChanges can persist their permanent deletion.
     MetahandleSet* const metahandles_to_purge;
 
     // TODO(ncarter): Figure out what the hell this is, and comment it.
     Channel* const channel;
 
-    // The listeners for directory change events, triggered when the
-    // transaction is ending.
-    ObserverList<DirectoryChangeListener> change_listeners_;
-
     KernelShareInfoStatus info_status;
 
     // These 3 members are backed in the share_info table, and
     // their state is marked by the flag above.
 
     // A structure containing the Directory state that is written back into the
     // database on SaveChanges.
     PersistedKernelInfo persisted_info;
 
     // A unique identifier for this account's cache db, used to generate
     // unique server IDs. No need to lock, only written at init time.
     std::string cache_guid;
 
     // It doesn't make sense for two threads to run SaveChanges at the same
     // time; this mutex protects that activity.
     base::Lock save_changes_mutex;
 
     // The next metahandle is protected by kernel mutex.
     int64 next_metahandle;
 
     // Keep a history of recently flushed metahandles for debugging
     // purposes.  Protected by the save_changes_mutex.
     DebugQueue<int64, 1000> flushed_metahandles;
+
+   private:
+    // The listeners for directory change events, triggered when the
+    // transaction is ending (and its lock).
+    base::Lock change_listeners_lock_;
+    ObserverList<DirectoryChangeListener> change_listeners_;
   };
 
   // Helper method used to do searches on |parent_id_child_index|.
   ParentIdChildIndex::iterator LocateInParentChildIndex(
       const ScopedKernelLock& lock,
       const Id& parent_id,
       int64 position_in_parent,
       const Id& item_id_for_tiebreaking);
 
   // Return an iterator to the beginning of the range of the children of
@@ skipping 114 matching lines @@
 
 // This is not a reset.  It just sets the numeric fields which are not
 // initialized by the constructor to zero.
 void ZeroFields(EntryKernel* entry, int first_field);
 
 }  // namespace syncable
 
 std::ostream& operator <<(std::ostream&, const syncable::Blob&);
 
 #endif  // CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_H_