[Sync] Make BackendMigrator not wait for full sync cycles

chrome/browser/sync/glue/sync_backend_host_mock.cc

Index: chrome/browser/sync/glue/sync_backend_host_mock.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host_mock.cc b/chrome/browser/sync/glue/sync_backend_host_mock.cc
index 1e5705ac0399f173c614f88b617005cc6351da4e..2d641f86a432255327ef710a080ff37988c5e547 100644
--- a/chrome/browser/sync/glue/sync_backend_host_mock.cc
+++ b/chrome/browser/sync/glue/sync_backend_host_mock.cc
@@ -7,6 +7,7 @@
 namespace browser_sync {
 
 using ::testing::_;
+using ::testing::Return;
 
 ACTION(InvokeTask) {
   arg3.Run(true);
@@ -16,6 +17,8 @@ SyncBackendHostMock::SyncBackendHostMock() {
   // By default, invoke the ready callback.
   ON_CALL(*this, ConfigureDataTypes(_, _, _, _, _)).
       WillByDefault(InvokeTask());
+  ON_CALL(*this, GetUnsyncedDataTypes()).
+      WillByDefault(Return(syncable::ModelTypeSet()));
 }
 
 SyncBackendHostMock::~SyncBackendHostMock() {}