Move FileEnumerator to its own file, do some refactoring.

chrome/browser/extensions/extension_service_unittest.cc

Index: chrome/browser/extensions/extension_service_unittest.cc
diff --git a/chrome/browser/extensions/extension_service_unittest.cc b/chrome/browser/extensions/extension_service_unittest.cc
index 7a79998298ba87a708a8fb5476e3146c9c2da533..b0706536e19f6694122108e3bee3359a1fcc04a3 100644
--- a/chrome/browser/extensions/extension_service_unittest.cc
+++ b/chrome/browser/extensions/extension_service_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/file_util.h"
+#include "base/files/file_enumerator.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_reader.h"
@@ -1317,8 +1318,8 @@ TEST_F(ExtensionServiceTest, CleanupOnStartup) {
   // Wait for GarbageCollectExtensions task to complete.
   loop_.RunUntilIdle();
 
-  file_util::FileEnumerator dirs(extensions_install_dir_, false,
-                                 file_util::FileEnumerator::DIRECTORIES);
+  base::FileEnumerator dirs(extensions_install_dir_, false,
+                            base::FileEnumerator::DIRECTORIES);
   size_t count = 0;
   while (!dirs.Next().empty())
     count++;