Update //third_party/protobuf to version 3.

third_party/protobuf/objectivec/Tests/unittest_cycle.proto

 // Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.  All rights reserved.
-// http://code.google.com/p/protobuf/
+// Copyright 2015 Google Inc.  All rights reserved.
 //
 // 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.
-//
-// A proto file which uses optimize_for = CODE_SIZE.
-
-import "google/protobuf/unittest.proto";
+syntax = "proto2";
 
 package protobuf_unittest;
 
-option optimize_for = CODE_SIZE;
+// Cycles in the Message graph can cause problems for the mutable classes
+// since the properties on the mutable class change types. This file just
+// needs to generate source, and that source must compile, to ensure the
+// generated source works for this sort of case.
 
-message TestOptimizedForSize {
-  optional int32 i = 1;
-  optional ForeignMessage msg = 19;
+// You can't make a object graph that spans files, so this can only be done
+// within a single proto file.
 
-  extensions 1000 to max;
-
-  extend TestOptimizedForSize {
-    optional int32 test_extension = 1234;
-    optional TestRequiredOptimizedForSize test_extension2 = 1235;
-  }
+message CycleFoo {
+  optional CycleFoo a_foo = 1;
+  optional CycleBar a_bar = 2;
+  optional CycleBaz a_baz = 3;
 }
 
-message TestRequiredOptimizedForSize {
-  required int32 x = 1;
+message CycleBar {
+  optional CycleBar a_bar = 1;
+  optional CycleBaz a_baz = 2;
+  optional CycleFoo a_foo = 3;
 }
- 
-message TestOptionalOptimizedForSize {
-  optional TestRequiredOptimizedForSize o = 1;
+
+message CycleBaz {
+  optional CycleBaz a_baz = 1;
+  optional CycleFoo a_foo = 2;
+  optional CycleBar a_bar = 3;
 }