Add callback list to PrefModelAssociator after sync data is loaded

components/syncable_prefs/pref_model_associator.h

Index: components/syncable_prefs/pref_model_associator.h
diff --git a/components/syncable_prefs/pref_model_associator.h b/components/syncable_prefs/pref_model_associator.h
index 6eaab7ef7bdb17f5a7db3008d0d824323531adfa..203c3e8f4f5e7ed6b0303dad9b12751017cfa98b 100644
--- a/components/syncable_prefs/pref_model_associator.h
+++ b/components/syncable_prefs/pref_model_associator.h
@@ -9,7 +9,9 @@
 #include <memory>
 #include <set>
 #include <string>
+#include <vector>
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
@@ -120,6 +122,10 @@ class PrefModelAssociator
   void SetPrefModelAssociatorClientForTesting(
       const PrefModelAssociatorClient* client);
 
+  // Register callback method which will get called at the end of
+  // PrefModelAssociator::MergeDataAndStartSyncing().
+  void RegisterMergeDataFinishedCallback(const base::Closure& callback);
+
  protected:
   friend class PrefServiceSyncableTest;
 
@@ -193,6 +199,8 @@ class PrefModelAssociator
   SyncedPrefObserverMap synced_pref_observers_;
   const PrefModelAssociatorClient* client_;  // Weak.
 
+  std::vector<base::Closure> callback_list_;

[pavely, 2016/07/06 22:11:56]

Check out CallbackList class. Maybe that's what you need here.

[lshang, 2016/07/07 08:26:05]

I did try to use CallbackList here at first, and add Subscription in
HostContentSettingsMap, which will deregister the callback when listener (here
is HostContentSettingsMap) gets destroyed. 

Problem is PrefModelAssociator gets destroyed first when sync is done, and
HostContentSettingsMap will last for longer time and gets destroyed when browser
closes, that will cause core dumped since the callback list has already been
destroyed. As in:
https://cs.chromium.org/chromium/src/base/callback_list.h?sq=package:chromium...

+
   DISALLOW_COPY_AND_ASSIGN(PrefModelAssociator);
 };