Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/objectivec/Tests/unittest_cycle.proto

-// Protocol Buffers - Google's data interchange format
-// 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.
-
-syntax = "proto2";
-
-package protobuf_unittest;
-
-// 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.
-
-// You can't make a object graph that spans files, so this can only be done
-// within a single proto file.
-
-message CycleFoo {
-  optional CycleFoo a_foo = 1;
-  optional CycleBar a_bar = 2;
-  optional CycleBaz a_baz = 3;
-}
-
-message CycleBar {
-  optional CycleBar a_bar = 1;
-  optional CycleBaz a_baz = 2;
-  optional CycleFoo a_foo = 3;
-}
-
-message CycleBaz {
-  optional CycleBaz a_baz = 1;
-  optional CycleFoo a_foo = 2;
-  optional CycleBar a_bar = 3;
-}