Update //third_party/protobuf to version 3.

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

Index: third_party/protobuf/python/google/protobuf/internal/message_set_extensions.proto
diff --git a/third_party/protobuf/src/google/protobuf/unittest_mset.proto b/third_party/protobuf/python/google/protobuf/internal/message_set_extensions.proto
similarity index 69%
copy from third_party/protobuf/src/google/protobuf/unittest_mset.proto
copy to third_party/protobuf/python/google/protobuf/internal/message_set_extensions.proto
index 3497f09fa6d41b7b38357e7f2610dfb5c087d3e4..14e5f1937518a0502f9f8c9ccde4e2f80f7eb4f4 100644
--- a/third_party/protobuf/src/google/protobuf/unittest_mset.proto
+++ b/third_party/protobuf/python/google/protobuf/internal/message_set_extensions.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 +28,11 @@
 // (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.
-//
-// This file contains messages for testing message_set_wire_format.
+// This file contains messages that extend MessageSet.
 
-package protobuf_unittest;
+syntax = "proto2";
+package google.protobuf.internal;
 
-option optimize_for = SPEED;
 
 // A message with message_set_wire_format.
 message TestMessageSet {
@@ -44,29 +40,35 @@ message TestMessageSet {
   extensions 4 to max;
 }
 
-message TestMessageSetContainer {
-  optional TestMessageSet message_set = 1;
-}
-
 message TestMessageSetExtension1 {
   extend TestMessageSet {
-    optional TestMessageSetExtension1 message_set_extension = 1545008;
+    optional TestMessageSetExtension1 message_set_extension = 98418603;
   }
   optional int32 i = 15;
 }
 
 message TestMessageSetExtension2 {
   extend TestMessageSet {
-    optional TestMessageSetExtension2 message_set_extension = 1547769;
+    optional TestMessageSetExtension2 message_set_extension = 98418634;
   }
   optional string str = 25;
 }
 
-// MessageSet wire format is equivalent to this.
-message RawMessageSet {
-  repeated group Item = 1 {
-    required int32 type_id = 2;
-    required bytes message = 3;
-  }
+message TestMessageSetExtension3 {
+  optional string text = 35;
+}
+
+extend TestMessageSet {
+  optional TestMessageSetExtension3 message_set_extension3 = 98418655;
 }
 
+// This message was used to generate
+// //net/proto2/python/internal/testdata/message_set_message, but is commented
+// out since it must not actually exist in code, to simulate an "unknown"
+// extension.
+// message TestMessageSetUnknownExtension {
+//   extend TestMessageSet {
+//     optional TestMessageSetUnknownExtension message_set_extension = 56141421;
+//   }
+//   optional int64 a = 1;
+// }