Add migration code to change existing domain scoped content settings to be origin scoped

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..c64a983942564fa863cb7b6fc4b7b42ecc3848fb 100644
--- a/components/syncable_prefs/pref_model_associator.h
+++ b/components/syncable_prefs/pref_model_associator.h
@@ -120,6 +120,9 @@ class PrefModelAssociator
   void SetPrefModelAssociatorClientForTesting(
       const PrefModelAssociatorClient* client);
 
+  static void SetMergeDataFinishedCallback(const base::Closure& callback);

[raymes, 2016/06/16 03:23:51]

I don't think we will want these to be static. Instead I think we will want to
get access to the PrefModelAssociator and add a listener.

We can get access to the PrefServiceSyncable from
syncable_prefs::PrefServiceSyncable* PrefServiceSyncableFromProfile() and
passing in the profile and then we could pass the callback down.

We should check with Pavel about all this because I'm just guessing :)

Usually it's good to write functions like this in a general way such that others
can reuse them. That usually means tracking a vector of callbacks in this class.
One way would be to have a function like this:

void AddMergeDataFinishedCallback(... callback) {
  if (merge_finished_) {
    callback.Run();
  else
    merge_finished_callbacks_.push_back(callback);
}

and then in the function where the merge finishes:

...
for (Callback callback : merge_finished_callbacks_)
  callback.Run();
merge_finished_callbacks_.clear();


Again we should probably run that by Pavel for his thoughts.

+  static void ResetMergeDataFinishedCallback();
+
  protected:
   friend class PrefServiceSyncableTest;
 
@@ -193,6 +196,8 @@ class PrefModelAssociator
   SyncedPrefObserverMap synced_pref_observers_;
   const PrefModelAssociatorClient* client_;  // Weak.
 
+  static base::Closure migrate_call_back_;
+
   DISALLOW_COPY_AND_ASSIGN(PrefModelAssociator);
 };