Move FileEnumerator to its own file, do some refactoring.

chrome/browser/extensions/api/serial/serial_port_enumerator_posix.cc

Index: chrome/browser/extensions/api/serial/serial_port_enumerator_posix.cc
diff --git a/chrome/browser/extensions/api/serial/serial_port_enumerator_posix.cc b/chrome/browser/extensions/api/serial/serial_port_enumerator_posix.cc
index ce29ea58ae360372a177535f34b6c9b6c741cce9..505d8b050625270437e82bc19a8e6b0a0cd89a4e 100644
--- a/chrome/browser/extensions/api/serial/serial_port_enumerator_posix.cc
+++ b/chrome/browser/extensions/api/serial/serial_port_enumerator_posix.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/extensions/api/serial/serial_port_enumerator.h"
 
 #include "base/file_util.h"
+#include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/string_util.h"
 #include "content/public/browser/browser_thread.h"
@@ -67,13 +68,12 @@ SerialPortEnumerator::GenerateValidSerialPortNames() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   const base::FilePath kDevRoot("/dev");
   const int kFilesAndSymLinks =
-      file_util::FileEnumerator::FILES |
-      file_util::FileEnumerator::SHOW_SYM_LINKS;
+      base::FileEnumerator::FILES |
+      base::FileEnumerator::SHOW_SYM_LINKS;
 
   StringSet valid_patterns = GenerateValidPatterns();
   StringSet name_set;
-  file_util::FileEnumerator enumerator(
-      kDevRoot, false, kFilesAndSymLinks);
+  base::FileEnumerator enumerator(kDevRoot, false, kFilesAndSymLinks);
   do {
     const base::FilePath next_device_path(enumerator.Next());
     const std::string next_device = next_device_path.value();