message: Use protobuf string wrapper in utility_test.cc.
  Required for Google import. The Protobuf::TextFormat::PrintToString
  method must use a wrapped string.
diff: +#include "common/protobuf/protobuf.h"
  #include "common/protobuf/utility.h"
  #include "test/test_common/environment.h"
  @@ -30,7 +31,7 @@ TEST(UtilityTest, LoadTextProtoFromFile) {
  ->mutable_source_address()
  ->set_address("1.1.1.1");
  - std::string bootstrap_text;
  + ProtobufTypes::String bootstrap_text;
  ASSERT_TRUE(Protobuf::TextFormat::PrintToString(bootstrap, &bootstrap_text));
  const std::string filename =
  TestEnvironment::writeStringToFileForTest("proto.pb_text", bootstrap_text);
  