Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/GPBUnknownFieldSet.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>
 
-#include <google/protobuf/io/zero_copy_stream.h>
+@class GPBUnknownField;
 
+NS_ASSUME_NONNULL_BEGIN
 
-namespace google {
-namespace protobuf {
-namespace io {
+@interface GPBUnknownFieldSet : NSObject<NSCopying>
 
-ZeroCopyInputStream::~ZeroCopyInputStream() {}
-ZeroCopyOutputStream::~ZeroCopyOutputStream() {}
+- (BOOL)hasField:(int32_t)number;
+- (nullable GPBUnknownField *)getField:(int32_t)number;
+- (NSUInteger)countOfFields;
 
+- (void)addField:(GPBUnknownField *)field;
 
-}  // namespace io
-}  // namespace protobuf
-}  // namespace google
+// Returns an NSArray of the GPBFields sorted by the field numbers.
+- (NSArray *)sortedFields;
+
+@end
+
+NS_ASSUME_NONNULL_END