Remove the migration code from content_settings::PrefProvider.

chrome/browser/prefs/pref_model_associator.cc

Index: chrome/browser/prefs/pref_model_associator.cc
diff --git a/chrome/browser/prefs/pref_model_associator.cc b/chrome/browser/prefs/pref_model_associator.cc
index 5ddbf1fbb937b8b7a3451b0e7255c7e144ec9b23..4a3bd1f5ce5e4fec86871544ec8a67d63d901274 100644
--- a/chrome/browser/prefs/pref_model_associator.cc
+++ b/chrome/browser/prefs/pref_model_associator.cc
@@ -16,6 +16,7 @@
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/prefs/pref_service_syncable.h"
 #include "chrome/common/pref_names.h"
+#include "components/content_settings/core/browser/content_settings_pref_provider.h"
 #include "sync/api/sync_change.h"
 #include "sync/api/sync_error_factory.h"
 #include "sync/protocol/preference_specifics.pb.h"
@@ -323,7 +324,7 @@ scoped_ptr<base::Value> PrefModelAssociator::MergePreference(
         MergeListValues(local_value, server_value)).Pass();
   }
 
-  if (name == prefs::kContentSettingsPatternPairs) {
+  if (content_settings::PrefProvider::IsContentSettingsExceptionsPref(name)) {

[msramek, 2015/07/27 17:53:01]

This change should have happened back at the time when we introduced these
preferences, not just now when we do the clean-up of the old news. 

However, I didn't know that merging of the local and synced dictionary needs to
be handled explicitly. Fortunately, this would only be a problem if the user
added two exceptions at different machines at the same time; one of them would
be ignored. Unsurprisingly, this is a rare enough case that no one has noticed.

     return scoped_ptr<base::Value>(
         MergeDictionaryValues(local_value, server_value)).Pass();
   }