sync: avoid creating a HistoryModelWorker unless it is needed.

chrome/browser/sync/test_profile_sync_service.h

Index: chrome/browser/sync/test_profile_sync_service.h
diff --git a/chrome/browser/sync/test_profile_sync_service.h b/chrome/browser/sync/test_profile_sync_service.h
index f5da3d6fa4d8634091804beab61568d23032b295..591ebcba895a26d3c0e8ad363c30b851e3a7b7fd 100644
--- a/chrome/browser/sync/test_profile_sync_service.h
+++ b/chrome/browser/sync/test_profile_sync_service.h
@@ -167,6 +167,9 @@ class SyncBackendHostForProfileSyncTest : public SyncBackendHost {
   static void SetDefaultExpectationsForWorkerCreation(ProfileMock* profile) {
     EXPECT_CALL(*profile, GetPasswordStore(testing::_)).
         WillOnce(testing::Return((PasswordStore*)NULL));
+  }
+
+  static void SetHistoryServiceExpectations(ProfileMock* profile) {
     EXPECT_CALL(*profile, GetHistoryService(testing::_)).
         WillOnce(testing::Return((HistoryService*)NULL));
   }