migrate delimited messages functions to util package

BUILD

diff --git a/BUILD b/BUILD
index bf89462..d34b32d 100644
--- a/BUILD
+++ b/BUILD
@@ -521,6 +521,7 @@
         "src/google/protobuf/stubs/type_traits_unittest.cc",
         "src/google/protobuf/text_format_unittest.cc",
         "src/google/protobuf/unknown_field_set_unittest.cc",
+        "src/google/protobuf/util/delimited_message_util_test.cc",
         "src/google/protobuf/util/field_comparator_test.cc",
         "src/google/protobuf/util/field_mask_util_test.cc",
         "src/google/protobuf/util/internal/default_value_objectwriter_test.cc",