wstring: use a few more FilePaths to remove Hack functions

chrome/installer/util/work_item.cc

Index: chrome/installer/util/work_item.cc
diff --git a/chrome/installer/util/work_item.cc b/chrome/installer/util/work_item.cc
index 546b9ebc4c7bd90ccad175dd360c0c3f6a833447..c62a38392d5abf0499f67696a0c9d2efaac3f345 100644
--- a/chrome/installer/util/work_item.cc
+++ b/chrome/installer/util/work_item.cc
@@ -23,11 +23,11 @@ WorkItem::~WorkItem() {
 }
 
 CopyTreeWorkItem* WorkItem::CreateCopyTreeWorkItem(
-    const std::wstring& source_path,
-    const std::wstring& dest_path,
-    const std::wstring& temp_dir,
+    const FilePath& source_path,
+    const FilePath& dest_path,
+    const FilePath& temp_dir,
     CopyOverWriteOption overwrite_option,
-    const std::wstring& alternative_path) {
+    const FilePath& alternative_path) {
   return new CopyTreeWorkItem(source_path, dest_path, temp_dir,
                               overwrite_option, alternative_path);
 }