Move ReadFileToString to the base namespace.

chromeos/network/client_cert_resolver_unittest.cc

Index: chromeos/network/client_cert_resolver_unittest.cc
diff --git a/chromeos/network/client_cert_resolver_unittest.cc b/chromeos/network/client_cert_resolver_unittest.cc
index 12ee8e69ddf78738f481c97ed7a4a70d90b9ea41..f275c825428d2d359458a2f67cb83f27b5ac9ba6 100644
--- a/chromeos/network/client_cert_resolver_unittest.cc
+++ b/chromeos/network/client_cert_resolver_unittest.cc
@@ -104,7 +104,7 @@ class ClientCertResolverTest : public testing::Test {
     // Import a client cert signed by that CA.
     scoped_refptr<net::CryptoModule> crypt_module = cert_db->GetPrivateModule();
     std::string pkcs12_data;
-    ASSERT_TRUE(file_util::ReadFileToString(
+    ASSERT_TRUE(base::ReadFileToString(
         net::GetTestCertsDirectory().Append("websocket_client_cert.p12"),
         &pkcs12_data));