implement things needed to run net/disk_cache/backend_unittest

base/file_util.h

Index: base/file_util.h
===================================================================
--- base/file_util.h	(revision 2109)
+++ base/file_util.h	(working copy)
@@ -132,6 +132,9 @@
 bool Move(const std::wstring& from_path, const std::wstring& to_path);
 
 // Copies a single file. Use CopyDirectory to copy directories.
+//
+// Behavior regarding attributes, permissions, metadata, etc is not guaranteed,
+// which means it may differ across platforms.
 bool CopyFile(const std::wstring& from_path, const std::wstring& to_path);
 
 // Copies the given path, and optionally all subdirectories and their contents
@@ -141,6 +144,9 @@
 // Dont't use wildcards on the names, it may stop working without notice.
 //
 // If you only need to copy a file use CopyFile, it's faster.
+//
+// Behavior regarding attributes, permissions, metadata, etc is not guaranteed,
+// which means it may differ across platforms.
 bool CopyDirectory(const std::wstring& from_path, const std::wstring& to_path,
                    bool recursive);