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

third_party/protobuf/python/google/protobuf/internal/factory_test1.proto

 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
-// https://developers.google.com/protocol-buffers/
+// http://code.google.com/p/protobuf/
 //
 // 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: matthewtoia@google.com (Matt Toia)
 
-syntax = "proto2";
 
 package google.protobuf.python.internal;
 
 
 enum Factory1Enum {
   FACTORY_1_VALUE_0 = 0;
   FACTORY_1_VALUE_1 = 1;
 }
 
 message Factory1Message {
   optional Factory1Enum factory_1_enum = 1;
   enum NestedFactory1Enum {
     NESTED_FACTORY_1_VALUE_0 = 0;
     NESTED_FACTORY_1_VALUE_1 = 1;
   }
   optional NestedFactory1Enum nested_factory_1_enum = 2;
   message NestedFactory1Message {
     optional string value = 1;
   }
   optional NestedFactory1Message nested_factory_1_message = 3;
   optional int32 scalar_value = 4;
   repeated string list_value = 5;
-
-  extensions 1000 to max;
 }