third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/java/util/src/test/proto/com/google/protobuf/util/json_test.proto

Index: third_party/protobuf/java/util/src/test/proto/com/google/protobuf/util/json_test.proto
diff --git a/third_party/protobuf/java/util/src/test/proto/com/google/protobuf/util/json_test.proto b/third_party/protobuf/java/util/src/test/proto/com/google/protobuf/util/json_test.proto
index 686edc422183d34d3a67130d112fa76d9bf6588e..a75338ef167ffc1c0d5540ee841ff5f2c03f4423 100644
--- a/third_party/protobuf/java/util/src/test/proto/com/google/protobuf/util/json_test.proto
+++ b/third_party/protobuf/java/util/src/test/proto/com/google/protobuf/util/json_test.proto
@@ -124,6 +124,7 @@ message TestOneof {
   oneof oneof_field {
     int32 oneof_int32 = 1;
     TestAllTypes.NestedMessage oneof_nested_message = 2;
+    google.protobuf.NullValue oneof_null_value = 3;
   }
 }
 
@@ -194,8 +195,14 @@ message TestStruct {
 
 message TestAny {
   google.protobuf.Any any_value = 1;
+  map<string, google.protobuf.Any> any_map = 2;
 }
 
 message TestCustomJsonName {
   int32 value = 1 [json_name = "@value"];
 }
+
+message TestRecursive {
+  int32 value = 1;
+  TestRecursive nested = 2;
+}