third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/patches/0008-uninline_get_empty_string.patch

-unchanged:
---- protobuf-cleaned/src/google/protobuf/generated_message_util.cc      2015-12-30 13:21:46.000000000 -0800
-+++ protobuf-patched/src/google/protobuf/generated_message_util.cc      2016-03-31 13:25:32.180017848 -0700
-@@ -60,6 +60,12 @@
-   OnShutdown(&DeleteEmptyString);
- }
- 
-+const ::std::string& GetEmptyString() {
-+  ::google::protobuf::GoogleOnceInit(&empty_string_once_init_, &InitEmptyString);
-+  return GetEmptyStringAlreadyInited();
-+}
-+
-+
- int StringSpaceUsedExcludingSelf(const string& str) {
-   const void* start = &str;
-   const void* end = &str + 1;
-only in patch2:
-unchanged:
---- protobuf-cleaned/src/google/protobuf/generated_message_util.h       2015-12-30 13:21:46.000000000 -0800
-+++ protobuf-patched/src/google/protobuf/generated_message_util.h       2016-03-31 13:25:40.252007316 -0700
-@@ -84,10 +84,8 @@
-   assert(empty_string_ != NULL);
-   return *empty_string_;
- }
--LIBPROTOBUF_EXPORT inline const ::std::string& GetEmptyString() {
--  ::google::protobuf::GoogleOnceInit(&empty_string_once_init_, &InitEmptyString);
--  return GetEmptyStringAlreadyInited();
--}
-+
-+LIBPROTOBUF_EXPORT const ::std::string& GetEmptyString();
- 
- LIBPROTOBUF_EXPORT int StringSpaceUsedExcludingSelf(const string& str);
-