Pull new version of protobuf sources.

third_party/protobuf/src/google/protobuf/unittest_import.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
@@ skipping 13 matching lines @@
 // 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 is imported by unittest.proto to test importing.
 
+syntax = "proto2";
 
 // We don't put this in a package within proto2 because we need to make sure
 // that the generated code doesn't depend on being in the proto2 namespace.
 // In test_util.h we do
 // "using namespace unittest_import = protobuf_unittest_import".
 package protobuf_unittest_import;
 
 option optimize_for = SPEED;
+option cc_enable_arenas = true;
 
-// Excercise the java_package option.
+// Exercise the java_package option.
 option java_package = "com.google.protobuf.test";
 
 // Do not set a java_outer_classname here to verify that Proto2 works without
 // one.
 
 // Test public import
 import public "google/protobuf/unittest_import_public.proto";
 
 message ImportMessage {
   optional int32 d = 1;
 }
 
 enum ImportEnum {
   IMPORT_FOO = 7;
   IMPORT_BAR = 8;
   IMPORT_BAZ = 9;
 }