sync: move invalidation version prefs out of SyncPrefs into InvalidatorStorage.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 92d38e32c84fd3ac6011ee6d3daefecd034ed22c..647cceab5cd265688e702ce8619ed2cf4064cd40 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1551,6 +1551,9 @@ const char kSyncMaxInvalidationVersions[] = "sync.max_invalidation_versions";
 // disable/enable events.
 const char kSyncSessionsGUID[] = "sync.session_sync_guid";
 
+// Opaque state from the invalidation subsystem that is persisted via prefs.
+const char kInvalidatorInvalidationState[] = "invalidator.invalidation_state";
+
 // A string that can be used to restore sync encryption infrastructure on
 // startup so that the user doesn't need to provide credentials on each start.
 const char kSyncEncryptionBootstrapToken[] =