Move ReadFileToString to the base namespace.

net/socket/ssl_client_socket_openssl_unittest.cc

Index: net/socket/ssl_client_socket_openssl_unittest.cc
diff --git a/net/socket/ssl_client_socket_openssl_unittest.cc b/net/socket/ssl_client_socket_openssl_unittest.cc
index 04f899903acc739b08f0fefa5cd2585c263560c5..24c06059be54cc63ea7d3de67ecf70e33828b3ce 100644
--- a/net/socket/ssl_client_socket_openssl_unittest.cc
+++ b/net/socket/ssl_client_socket_openssl_unittest.cc
@@ -67,7 +67,7 @@ bool LoadPrivateKeyOpenSSL(
     const base::FilePath& filepath,
     OpenSSLClientKeyStore::ScopedEVP_PKEY* pkey) {
   std::string data;
-  if (!file_util::ReadFileToString(filepath, &data)) {
+  if (!base::ReadFileToString(filepath, &data)) {
     LOG(ERROR) << "Could not read private key file: "
                << filepath.value() << ": " << strerror(errno);
     return false;