Move ReadFileToString to the base namespace.

chrome/browser/chromeos/system/automatic_reboot_manager_unittest.cc

Index: chrome/browser/chromeos/system/automatic_reboot_manager_unittest.cc
diff --git a/chrome/browser/chromeos/system/automatic_reboot_manager_unittest.cc b/chrome/browser/chromeos/system/automatic_reboot_manager_unittest.cc
index 6f76b354b2ef578845f37d6b2e78668ea0a33fda..7aac719cfaf012041d696df5b2564ae5035f7af9 100644
--- a/chrome/browser/chromeos/system/automatic_reboot_manager_unittest.cc
+++ b/chrome/browser/chromeos/system/automatic_reboot_manager_unittest.cc
@@ -478,8 +478,7 @@ void AutomaticRebootManagerBasicTest::CreateAutomaticRebootManager(
 bool AutomaticRebootManagerBasicTest::ReadUpdateRebootNeededUptimeFromFile(
     base::TimeDelta* uptime) {
   std::string contents;
-  if (!file_util::ReadFileToString(update_reboot_needed_uptime_file_,
-                                   &contents)) {
+  if (!base::ReadFileToString(update_reboot_needed_uptime_file_, &contents)) {
     return false;
   }
   double seconds;