Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/unittest_import_proto3.proto

Index: third_party/protobuf/src/google/protobuf/unittest_import_proto3.proto
diff --git a/third_party/protobuf/src/google/protobuf/unittest_import.proto b/third_party/protobuf/src/google/protobuf/unittest_import_proto3.proto
similarity index 85%
copy from third_party/protobuf/src/google/protobuf/unittest_import.proto
copy to third_party/protobuf/src/google/protobuf/unittest_import_proto3.proto
index c115b11171afaa03d7ee6aeedc7506689cfd7038..59673eaf9d43bd15e89d2a05f2b920a7824cba1e 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_import.proto
+++ b/third_party/protobuf/src/google/protobuf/unittest_import_proto3.proto
@@ -1,6 +1,6 @@
 // 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
@@ -32,8 +32,9 @@
 //  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.
+// A proto file which is imported by unittest_proto3.proto to test importing.
 
+syntax = "proto3";
 
 // 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.
@@ -42,21 +43,24 @@
 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";
+option csharp_namespace = "Google.Protobuf.TestProtos";
 
 // 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";
+import public "google/protobuf/unittest_import_public_proto3.proto";
 
 message ImportMessage {
-  optional int32 d = 1;
+  int32 d = 1;
 }
 
 enum ImportEnum {
+  IMPORT_ENUM_UNSPECIFIED = 0;
   IMPORT_FOO = 7;
   IMPORT_BAR = 8;
   IMPORT_BAZ = 9;