Move ReadFileToString to the base namespace.

chromeos/system/name_value_pairs_parser.cc

Index: chromeos/system/name_value_pairs_parser.cc
diff --git a/chromeos/system/name_value_pairs_parser.cc b/chromeos/system/name_value_pairs_parser.cc
index 091e1fc346836d8327f6dcc7972513956f87668f..31ba010de1fa1c68f33a1475430b76ec1842a3fa 100644
--- a/chromeos/system/name_value_pairs_parser.cc
+++ b/chromeos/system/name_value_pairs_parser.cc
@@ -123,7 +123,7 @@ bool NameValuePairsParser::GetNameValuePairsFromFile(
     const std::string& eq,
     const std::string& delim) {
   std::string contents;
-  if (file_util::ReadFileToString(file_path, &contents)) {
+  if (base::ReadFileToString(file_path, &contents)) {
     return ParseNameValuePairs(contents, eq, delim);
   } else {
     LOG(WARNING) << "Unable to read statistics file: " << file_path.value();