sync: Move migration signal out of snapshot

sync/engine/sync_scheduler_impl.cc

Index: sync/engine/sync_scheduler_impl.cc
diff --git a/sync/engine/sync_scheduler_impl.cc b/sync/engine/sync_scheduler_impl.cc
index 13993313a36f3019bbdc8035ec28b4ccd26441a6..09e841f2cba178a1bfb564bb9760f666d5bad35b 100644
--- a/sync/engine/sync_scheduler_impl.cc
+++ b/sync/engine/sync_scheduler_impl.cc
@@ -906,6 +906,12 @@ void SyncSchedulerImpl::OnReceivedGuRetryDelay(const base::TimeDelta& delay) {
                      &SyncSchedulerImpl::RetryTimerCallback);
 }
 
+void SyncSchedulerImpl::OnReceivedMigrationRequest(ModelTypeSet types) {
+    FOR_EACH_OBSERVER(SyncEngineEventListener,
+                      *session_context_->listeners(),
+                      OnMigrationRequested(types));
+}
+
 void SyncSchedulerImpl::SetNotificationsEnabled(bool notifications_enabled) {
   DCHECK(CalledOnValidThread());
   session_context_->set_notifications_enabled(notifications_enabled);