Move FileEnumerator to its own file, do some refactoring.

net/tools/quic/quic_in_memory_cache.cc

Index: net/tools/quic/quic_in_memory_cache.cc
diff --git a/net/tools/quic/quic_in_memory_cache.cc b/net/tools/quic/quic_in_memory_cache.cc
index b4061266f32acd8b694fa3249beca43a2d7fa3b5..0de0bc0d48f0dae88c0814c474f8c89cf990ead4 100644
--- a/net/tools/quic/quic_in_memory_cache.cc
+++ b/net/tools/quic/quic_in_memory_cache.cc
@@ -5,11 +5,11 @@
 #include "net/tools/quic/quic_in_memory_cache.h"
 
 #include "base/file_util.h"
+#include "base/files/file_enumerator.h"
 #include "base/stl_util.h"
 
 using base::FilePath;
 using base::StringPiece;
-using file_util::FileEnumerator;
 using std::string;
 
 // Specifies the directory used during QuicInMemoryCache
@@ -120,9 +120,9 @@ QuicInMemoryCache::QuicInMemoryCache() {
             << FLAGS_quic_in_memory_cache_dir;
 
   FilePath directory(FLAGS_quic_in_memory_cache_dir);
-  FileEnumerator file_list(directory,
-                           true,
-                           FileEnumerator::FILES);
+  base::FileEnumerator file_list(directory,
+                                 true,
+                                 base::FileEnumerator::FILES);
 
   FilePath file = file_list.Next();
   while (!file.empty()) {