Update //third_party/protobuf to version 3.

third_party/protobuf/src/google/protobuf/unittest_arena.proto

Index: third_party/protobuf/src/google/protobuf/unittest_arena.proto
diff --git a/third_party/protobuf/src/google/protobuf/unittest_import_public_lite.proto b/third_party/protobuf/src/google/protobuf/unittest_arena.proto
similarity index 80%
copy from third_party/protobuf/src/google/protobuf/unittest_import_public_lite.proto
copy to third_party/protobuf/src/google/protobuf/unittest_arena.proto
index d077563cbd84d7be6daddec3f553cb564f23da0a..cd7e437e163e1a2e3442869a5623973f9251ebc6 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_import_public_lite.proto
+++ b/third_party/protobuf/src/google/protobuf/unittest_arena.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
@@ -28,15 +28,19 @@
 // (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: liujisi@google.com (Pherl Liu)
+syntax = "proto2";
 
+import "google/protobuf/unittest_no_arena_import.proto";
 
-package protobuf_unittest_import;
+package proto2_arena_unittest;
 
-option optimize_for = LITE_RUNTIME;
+option cc_enable_arenas = true;
 
-option java_package = "com.google.protobuf";
-
-message PublicImportMessageLite {
-  optional int32 e = 1;
+message NestedMessage {
+  optional int32 d = 1;
 }
+
+message ArenaMessage {
+  repeated NestedMessage  repeated_nested_message = 1;
+  repeated ImportNoArenaNestedMessage  repeated_import_no_arena_message = 2;
+};