Move FileEnumerator to its own file, do some refactoring.

chrome/installer/util/shell_util.cc

Index: chrome/installer/util/shell_util.cc
diff --git a/chrome/installer/util/shell_util.cc b/chrome/installer/util/shell_util.cc
index 37876e5856f19c36bc88e104f5109f627abf689c..59a9dce60cbde607c054a484cbf7f5045f64ed4c 100644
--- a/chrome/installer/util/shell_util.cc
+++ b/chrome/installer/util/shell_util.cc
@@ -18,6 +18,7 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/file_util.h"
+#include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ -1231,8 +1232,8 @@ bool BatchShortcutAction(const FileOperationCallback& shortcut_operation,
 
   bool success = true;
   InstallUtil::ProgramCompare target_compare(target_exe);
-  file_util::FileEnumerator enumerator(
-      shortcut_folder, false, file_util::FileEnumerator::FILES,
+  base::FileEnumerator enumerator(
+      shortcut_folder, false, base::FileEnumerator::FILES,
       string16(L"*") + installer::kLnkExt);
   base::FilePath target_path;
   for (base::FilePath shortcut_path = enumerator.Next();