Move FileEnumerator to its own file, do some refactoring.

net/base/directory_lister.h

Index: net/base/directory_lister.h
diff --git a/net/base/directory_lister.h b/net/base/directory_lister.h
index 999b8577dba6b7bf5f33cda886871a3bccd4e385..e8de0ab4c31fbf65837d8821a6e52ba2da3b85b5 100644
--- a/net/base/directory_lister.h
+++ b/net/base/directory_lister.h
@@ -7,7 +7,7 @@
 
 #include <vector>
 
-#include "base/file_util.h"
+#include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop_proxy.h"
@@ -26,7 +26,7 @@ class NET_EXPORT DirectoryLister  {
  public:
   // Represents one file found.
   struct DirectoryListerData {
-    file_util::FileEnumerator::FindInfo info;
+    base::FileEnumerator::FileInfo info;
     base::FilePath path;
   };