sync: Move migration signal out of snapshot

chrome/browser/sync/glue/sync_backend_host_core.cc

Index: chrome/browser/sync/glue/sync_backend_host_core.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host_core.cc b/chrome/browser/sync/glue/sync_backend_host_core.cc
index 8d7d4a7ce4749844869833b104e7b5214de3fdbd..00543a445ed9fbd0cd6ffac82c16520496accb4a 100644
--- a/chrome/browser/sync/glue/sync_backend_host_core.cc
+++ b/chrome/browser/sync/glue/sync_backend_host_core.cc
@@ -317,6 +317,14 @@ void SyncBackendHostCore::OnActionableError(
       sync_error);
 }
 
+void SyncBackendHostCore::OnMigrationRequested(syncer::ModelTypeSet types) {
+  DCHECK_EQ(base::MessageLoop::current(), sync_loop_);
+  host_.Call(
+      FROM_HERE,
+      &SyncBackendHostImpl::HandleMigrationRequestedOnFrontendLoop,
+      types);
+}
+
 void SyncBackendHostCore::DoOnInvalidatorStateChange(
     syncer::InvalidatorState state) {
   DCHECK_EQ(base::MessageLoop::current(), sync_loop_);