wstring: use a few more FilePaths to remove Hack functions

chrome/installer/util/work_item_list.cc

Index: chrome/installer/util/work_item_list.cc
diff --git a/chrome/installer/util/work_item_list.cc b/chrome/installer/util/work_item_list.cc
index 28e28292f7e427a1f903ea73996859d68aa5849b..05c0b583c39030e07c1623f8f1d3cacbf86d94b6 100644
--- a/chrome/installer/util/work_item_list.cc
+++ b/chrome/installer/util/work_item_list.cc
@@ -78,11 +78,11 @@ WorkItem* WorkItemList::AddCopyTreeWorkItem(
     const std::wstring& temp_dir,
     CopyOverWriteOption overwrite_option,
     const std::wstring& alternative_path) {
-  WorkItem* item = WorkItem::CreateCopyTreeWorkItem(source_path,
-                                                    dest_path,
-                                                    temp_dir,
+  WorkItem* item = WorkItem::CreateCopyTreeWorkItem(FilePath(source_path),
+                                                    FilePath(dest_path),
+                                                    FilePath(temp_dir),
                                                     overwrite_option,
-                                                    alternative_path);
+                                                    FilePath(alternative_path));
   AddWorkItem(item);
   return item;
 }