Extension settings API: send ACTION_UPDATE rather than ACTION_ADD when a

chrome/browser/extensions/syncable_extension_settings_storage.cc

Index: chrome/browser/extensions/syncable_extension_settings_storage.cc
diff --git a/chrome/browser/extensions/syncable_extension_settings_storage.cc b/chrome/browser/extensions/syncable_extension_settings_storage.cc
index 8ec5d178941d6d24a1bd4d8bcc4cdbdc46492e49..95e73f75374322323293e93cbadd9714ca7e77ca 100644
--- a/chrome/browser/extensions/syncable_extension_settings_storage.cc
+++ b/chrome/browser/extensions/syncable_extension_settings_storage.cc
@@ -182,6 +182,9 @@ SyncError SyncableExtensionSettingsStorage::OverwriteLocalSettingsWithSync(
                 extension_id_,
                 *it,
                 sync_value.release()));
+      } else {
+        // Sync and local values are the same, no changes to send.
+        synced_keys_.insert(*it);
       }
     } else {
       // Not synced, delete local setting.