Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/GPBExtensionInternals.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: jasonh@google.com (Jason Hsueh)
-//
-// This file is used to test a corner case in the CPP implementation where the
-// generated C++ type is available for the extendee, but the extension is
-// defined in a file whose C++ type is not in the binary.
+#import <Foundation/Foundation.h>
 
+#import "GPBDescriptor.h"
 
-import "google/protobuf/internal/more_extensions.proto";
+@class GPBCodedInputStream;
+@class GPBCodedOutputStream;
+@class GPBExtensionRegistry;
 
-package google.protobuf.internal;
+void GPBExtensionMergeFromInputStream(GPBExtensionDescriptor *extension,
+                                      BOOL isPackedOnStream,
+                                      GPBCodedInputStream *input,
+                                      GPBExtensionRegistry *extensionRegistry,
+                                      GPBMessage *message);
 
-message DynamicMessageType {
-  optional int32 a = 1;
-}
+size_t GPBComputeExtensionSerializedSizeIncludingTag(
+    GPBExtensionDescriptor *extension, id value);
 
-extend ExtendedMessage {
-  optional int32 dynamic_int32_extension = 100;
-  optional DynamicMessageType dynamic_message_extension = 101;
-}
+void GPBWriteExtensionValueToOutputStream(GPBExtensionDescriptor *extension,
+                                          id value,
+                                          GPBCodedOutputStream *output);