Replace changes_channel with an observer list.

chrome/browser/sync/engine/syncer.h

 // 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_ENGINE_SYNCER_H_
 #define CHROME_BROWSER_SYNC_ENGINE_SYNCER_H_
 
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 58 matching lines @@
 // to SyncShare() may take an unbounded amount of time, as SyncerCommands
 // may block on network i/o, on lock contention, or on tasks posted to
 // other threads.
 class Syncer {
  public:
   typedef std::vector<int64> UnsyncedMetaHandles;
 
   // The constructor may be called from a thread that is not the Syncer's
   // dedicated thread, to allow some flexibility in the setup.
   explicit Syncer(sessions::SyncSessionContext* context);
-  ~Syncer() {}
+  ~Syncer();
 
   // Called by other threads to tell the syncer to stop what it's doing
   // and return early from SyncShare, if possible.
   bool ExitRequested() {
     AutoLock lock(early_exit_requested_lock_);
     return early_exit_requested_;
   }
   void RequestEarlyExit() {
     AutoLock lock(early_exit_requested_lock_);
     early_exit_requested_ = true;
@@ skipping 116 matching lines @@
   }
   return false;
 }
 // Utility function declarations.
 void CopyServerFields(syncable::Entry* src, syncable::MutableEntry* dest);
 void ClearServerData(syncable::MutableEntry* entry);
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_SYNCER_H_