[Sync] Make BackendMigrator not wait for full sync cycles

chrome/test/live_sync/live_sync_test.h

Index: chrome/test/live_sync/live_sync_test.h
diff --git a/chrome/test/live_sync/live_sync_test.h b/chrome/test/live_sync/live_sync_test.h
index 9c848f920542d990d22b5d7ede023490bf1e8bbd..89f7edc082c6b21f80a5e9c7c94e1b1e7c307372 100644
--- a/chrome/test/live_sync/live_sync_test.h
+++ b/chrome/test/live_sync/live_sync_test.h
@@ -142,19 +142,23 @@ class LiveSyncTest : public InProcessBrowserTest {
 
   // Returns true if the server being used supports controlling
   // notifications.
-  bool ServerSupportsNotificationControl();
+  bool ServerSupportsNotificationControl() const;
 
   // Disable notifications on the server.  This operation is available
   // only if ServerSupportsNotificationControl() returned true.
   void DisableNotifications();
 
+  // Enable notifications on the server.  This operation is available
+  // only if ServerSupportsNotificationControl() returned true.
+  void EnableNotifications();
+
   // Trigger a notification to be sent to all clients.  This operation
   // is available only if ServerSupportsNotificationControl() returned
   // true.
   void TriggerNotification(const syncable::ModelTypeSet& changed_types);
 
   // Returns true if the server being used supports injecting errors.
-  bool ServerSupportsErrorTriggering();
+  bool ServerSupportsErrorTriggering() const;
 
   // Triggers a migration for one or more datatypes, and waits
   // for the server to complete it.  This operation is available