Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/compiler/test_plugin.cc

 // 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 28 matching lines @@
 int main(int argc, char* argv[]) {
 #ifdef _MSC_VER
   // Don't print a silly message or stick a modal dialog box in my face,
   // please.
   _set_abort_behavior(0, ~0);
 #endif  // !_MSC_VER
 
   google::protobuf::compiler::MockCodeGenerator generator("test_plugin");
   return google::protobuf::compiler::PluginMain(argc, argv, &generator);
 }