Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/Tests/unittest_objc_startup.proto

 // 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)
+syntax = "proto2";
 
-package google.protobuf.no_generic_services_test;
+package protobuf_objc_unittest;
 
-// *_generic_services are false by default.
-
-message TestMessage {
-  optional int32 a = 1;
-  extensions 1000 to max;
+message TestObjCStartupMessage {
+  extensions 1 to max;
 }
 
-enum TestEnum {
-  FOO = 1;
+extend TestObjCStartupMessage {
+  // Singular
+  optional    int32 optional_int32_extension    = 1;
+  repeated    int32 repeated_int32_extension    = 2;
 }
 
-extend TestMessage {
-  optional int32 test_extension = 1000;
+message TestObjCStartupNested {
+  extend TestObjCStartupMessage {
+    optional string nested_string_extension = 3;
+  }
 }
-
-service TestService {
-  rpc Foo(TestMessage) returns(TestMessage);
-}