Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_tsan.h

 // Protocol Buffers - Google's data interchange format
 // Copyright 2013 Google Inc.  All rights reserved.
-// http://code.google.com/p/protobuf/
+// https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
 // in the documentation and/or other materials provided with the
@@ skipping 196 matching lines @@
   __tsan_atomic_thread_fence(__tsan_memory_order_seq_cst);
 }
 
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
 
 #undef ATOMICOPS_COMPILER_BARRIER
 
 #endif  // GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_TSAN_H_