third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/js/test2.proto

Index: third_party/protobuf/js/test2.proto
diff --git a/third_party/protobuf/js/test2.proto b/third_party/protobuf/js/test2.proto
index 44e55effcb47e983729f41a0b95f3e0f20497c05..b67f93fa9ece8e72ed4744461afd435ba03bfaff 100644
--- a/third_party/protobuf/js/test2.proto
+++ b/third_party/protobuf/js/test2.proto
@@ -35,6 +35,8 @@ option java_multiple_files = true;
 
 package jspb.test;
 
+import "test.proto";
+
 message TestExtensionsMessage {
   optional int32 intfield = 1;
   extensions 100 to max;
@@ -52,3 +54,7 @@ extend TestExtensionsMessage {
   optional ExtensionMessage floating_msg_field = 101;
   optional string floating_str_field = 102;
 }
+
+message ForeignNestedFieldMessage {
+  optional Deeply.Nested.Message deeply_nested_message = 1;
+}