Cleanup: Pass std::string as const reference if possible

chrome/browser/sync/profile_sync_service_bookmark_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // TODO(akalin): This file is basically just a unit test for
 // BookmarkChangeProcessor.  Write unit tests for
 // BookmarkModelAssociator separately.
 
 #include <map>
 #include <queue>
@@ skipping 362 matching lines @@
   }
 
   // Inserts a folder directly to the share.
   // Do not use this after model association is complete.
   //
   // This function differs from the AddFolder() function declared elsewhere in
   // this file in that it only affects the sync model.  It would be invalid to
   // change the sync model directly after ModelAssociation.  This function can
   // be invoked prior to model association to set up first-time sync model
   // association scenarios.
-  int64 AddFolderToShare(syncer::WriteTransaction* trans, std::string title) {
+  int64 AddFolderToShare(syncer::WriteTransaction* trans,
+                         const std::string& title) {
     EXPECT_FALSE(model_associator_);
 
     // Be sure to call CreatePermanentBookmarkNodes(), otherwise this will fail.
     syncer::ReadNode bookmark_bar(trans);
     EXPECT_EQ(BaseNode::INIT_OK,
               bookmark_bar.InitByTagLookupForBookmarks("bookmark_bar"));
 
     syncer::WriteNode node(trans);
     EXPECT_TRUE(node.InitBookmarkByCreation(bookmark_bar, NULL));
     node.SetIsFolder(true);
@@ skipping 2206 matching lines @@
   EXPECT_EQ(syncer::kInvalidId, sync_id);
 
   // Verify that Sync ignores deleting this node.
   model_->Remove(node);
   EXPECT_EQ(sync_bookmark_count, GetSyncBookmarkCount());
 }
 
 }  // namespace
 
 }  // namespace browser_sync