Move ReadFileToString to the base namespace.

chrome/browser/net/firefox_proxy_settings.cc

Index: chrome/browser/net/firefox_proxy_settings.cc
diff --git a/chrome/browser/net/firefox_proxy_settings.cc b/chrome/browser/net/firefox_proxy_settings.cc
index aece777dbb84efae3ebe2e7a59812fa8d0f5f45e..9df1dda5badb2132088995608eb5b679d858f2f0 100644
--- a/chrome/browser/net/firefox_proxy_settings.cc
+++ b/chrome/browser/net/firefox_proxy_settings.cc
@@ -69,7 +69,7 @@ bool ParsePrefFile(const base::FilePath& pref_file, DictionaryValue* prefs) {
   // The string that is before a pref key.
   const std::string kUserPrefString = "user_pref(\"";
   std::string contents;
-  if (!file_util::ReadFileToString(pref_file, &contents))
+  if (!base::ReadFileToString(pref_file, &contents))
     return false;
 
   std::vector<std::string> lines;