third_party/protobuf: update to upstream r371

third_party/protobuf/src/google/protobuf/generated_message_util.h

Index: third_party/protobuf/src/google/protobuf/generated_message_util.h
diff --git a/third_party/protobuf/src/google/protobuf/generated_message_util.h b/third_party/protobuf/src/google/protobuf/generated_message_util.h
index daa16f7748e4aa517f2560b6ed08ea68d7ce8baa..1a2343d440838e8190643edab2fc3b0e7f81f7e9 100644
--- a/third_party/protobuf/src/google/protobuf/generated_message_util.h
+++ b/third_party/protobuf/src/google/protobuf/generated_message_util.h
@@ -38,6 +38,8 @@
 #ifndef GOOGLE_PROTOBUF_GENERATED_MESSAGE_UTIL_H__
 #define GOOGLE_PROTOBUF_GENERATED_MESSAGE_UTIL_H__
 
+#include <string>
+
 #include <google/protobuf/stubs/common.h>
 
 
@@ -66,8 +68,11 @@ namespace internal {
 
 
 // Constants for special floating point values.
-LIBPROTOBUF_EXPORT double Infinity();
-LIBPROTOBUF_EXPORT double NaN();
+double Infinity();
+double NaN();
+
+// Constant used for empty default strings.
+extern const ::std::string kEmptyString;
 
 
 }  // namespace internal