Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/GPBExtensionRegistry.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
 // distribution.
 //     * Neither the name of Google Inc. nor the names of its
 // contributors may be used to endorse or promote products derived from
 // this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Author: kenton@google.com (Kenton Varda)
-//  Based on original Protocol Buffers design by
-//  Sanjay Ghemawat, Jeff Dean, and others.
+#import <Foundation/Foundation.h>
+
+@class GPBDescriptor;
+@class GPBExtensionDescriptor;
+
+NS_ASSUME_NONNULL_BEGIN
+
+// A table of known extensions, searchable by name or field number.  When
+// parsing a protocol message that might have extensions, you must provide an
+// ExtensionRegistry in which you have registered any extensions that you want
+// to be able to parse.  Otherwise, those extensions will just be treated like
+// unknown fields.
 //
-// Generates Java code for a given .proto file.
+// The *Root classes provide +extensionRegistry for the extensions defined in a
+// given file *and* all files it imports.  You can also create a
+// GPBExtensionRegistry, and merge those registries to handle parsing extensions
+// defined from non overlapping files.
+//
+//    GPBExtensionRegistry *registry =
+//        [[[MyProtoFileRoot extensionRegistry] copy] autorelease];
+//    [registry addExtension:[OtherMessage neededExtension];  // Not in MyProtoFile
+//    NSError *parseError = nil;
+//    MyMessage *msg = [MyMessage parseData:data
+//                        extensionRegistry:registry
+//                                    error:&parseError];
+//
+@interface GPBExtensionRegistry : NSObject<NSCopying>
 
-#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_GENERATOR_H__
-#define GOOGLE_PROTOBUF_COMPILER_JAVA_GENERATOR_H__
+- (void)addExtension:(GPBExtensionDescriptor *)extension;
+- (void)addExtensions:(GPBExtensionRegistry *)registry;
 
-#include <string>
-#include <google/protobuf/compiler/code_generator.h>
+- (nullable GPBExtensionDescriptor *)extensionForDescriptor:(GPBDescriptor *)descriptor
+                                                fieldNumber:(NSInteger)fieldNumber;
 
-namespace google {
-namespace protobuf {
-namespace compiler {
-namespace java {
+@end
 
-// CodeGenerator implementation which generates Java code.  If you create your
-// own protocol compiler binary and you want it to support Java output, you
-// can do so by registering an instance of this CodeGenerator with the
-// CommandLineInterface in your main() function.
-class LIBPROTOC_EXPORT JavaGenerator : public CodeGenerator {
- public:
-  JavaGenerator();
-  ~JavaGenerator();
-
-  // implements CodeGenerator ----------------------------------------
-  bool Generate(const FileDescriptor* file,
-                const string& parameter,
-                GeneratorContext* context,
-                string* error) const;
-
- private:
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(JavaGenerator);
-};
-
-}  // namespace java
-}  // namespace compiler
-}  // namespace protobuf
-
-}  // namespace google
-#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_GENERATOR_H__
+NS_ASSUME_NONNULL_END