Move ReadFileToString to the base namespace.

chrome/test/perf/tab_switching_test.cc

Index: chrome/test/perf/tab_switching_test.cc
diff --git a/chrome/test/perf/tab_switching_test.cc b/chrome/test/perf/tab_switching_test.cc
index 8ddfb210b50636bc0d43662b8398511932da1691..55a4d085bfc12b0c34fa41193935e7b69978f606 100644
--- a/chrome/test/perf/tab_switching_test.cc
+++ b/chrome/test/perf/tab_switching_test.cc
@@ -113,8 +113,7 @@ class TabSwitchingUITest : public UIPerfTest {
       std::string contents;
       int max_tries = 20;
       do {
-        log_has_been_dumped = file_util::ReadFileToString(log_file_name_,
-                                                          &contents);
+        log_has_been_dumped = base::ReadFileToString(log_file_name_, &contents);
         if (!log_has_been_dumped)
           base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(100));
       } while (!log_has_been_dumped && max_tries--);