Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_extension.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 36 matching lines @@
 namespace protobuf {
 namespace compiler {
 namespace cpp {
 
 // Generates code for an extension, which may be within the scope of some
 // message or may be at file scope.  This is much simpler than FieldGenerator
 // since extensions are just simple identifiers with interesting types.
 class ExtensionGenerator {
  public:
   // See generator.cc for the meaning of dllexport_decl.
-  explicit ExtensionGenerator(const FieldDescriptor* desycriptor,
+  explicit ExtensionGenerator(const FieldDescriptor* descriptor,
                               const Options& options);
   ~ExtensionGenerator();
 
   // Header stuff.
   void GenerateDeclaration(io::Printer* printer);
 
   // Source file stuff.
   void GenerateDefinition(io::Printer* printer);
 
   // Generate code to register the extension.
   void GenerateRegistration(io::Printer* printer);
 
  private:
   const FieldDescriptor* descriptor_;
   string type_traits_;
   Options options_;
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ExtensionGenerator);
 };
 
 }  // namespace cpp
 }  // namespace compiler
 }  // namespace protobuf
 
 }  // namespace google
 #endif  // GOOGLE_PROTOBUF_COMPILER_CPP_MESSAGE_H__