Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/compiler/subprocess.h

 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 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 32 matching lines @@
 
 
 namespace google {
 namespace protobuf {
 
 class Message;
 
 namespace compiler {
 
 // Utility class for launching sub-processes.
-class Subprocess {
+class LIBPROTOC_EXPORT Subprocess {
  public:
   Subprocess();
   ~Subprocess();
 
   enum SearchMode {
     SEARCH_PATH,   // Use PATH environment variable.
     EXACT_NAME     // Program is an exact file name; don't use the PATH.
   };
 
   // Start the subprocess.  Currently we don't provide a way to specify
@@ skipping 32 matching lines @@
   int child_stdout_;
 
 #endif  // !_WIN32
 };
 
 }  // namespace compiler
 }  // namespace protobuf
 
 }  // namespace google
 #endif  // GOOGLE_PROTOBUF_COMPILER_SUBPROCESS_H__