Move WriteFile and WriteFileDescriptor from file_util to base namespace.

chrome/browser/chromeos/app_mode/kiosk_app_update_service_browsertest.cc

Index: chrome/browser/chromeos/app_mode/kiosk_app_update_service_browsertest.cc
diff --git a/chrome/browser/chromeos/app_mode/kiosk_app_update_service_browsertest.cc b/chrome/browser/chromeos/app_mode/kiosk_app_update_service_browsertest.cc
index 867510382d7499600f4007ad618b7576b7492013..89234a0f02bde259d42c775f870b161631a67813 100644
--- a/chrome/browser/chromeos/app_mode/kiosk_app_update_service_browsertest.cc
+++ b/chrome/browser/chromeos/app_mode/kiosk_app_update_service_browsertest.cc
@@ -52,7 +52,7 @@ class KioskAppUpdateServiceTest : public extensions::PlatformAppBrowserTest {
         base::DoubleToString(uptime.InSecondsF());
     const base::FilePath uptime_file = temp_dir.Append("uptime");
     ASSERT_EQ(static_cast<int>(uptime_seconds.size()),
-              file_util::WriteFile(
+              base::WriteFile(
                   uptime_file, uptime_seconds.c_str(), uptime_seconds.size()));
     uptime_file_override_.reset(
         new base::ScopedPathOverride(chromeos::FILE_UPTIME, uptime_file));