diff --git a/vendor/google.golang.org/protobuf/internal/impl/convert_list.go b/vendor/google.golang.org/protobuf/internal/impl/convert_list.go
new file mode 100644
index 0000000..6fccab5
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/convert_list.go
@@ -0,0 +1,141 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package impl
+
+import (
+	"fmt"
+	"reflect"
+
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+)
+
+func newListConverter(t reflect.Type, fd pref.FieldDescriptor) Converter {
+	switch {
+	case t.Kind() == reflect.Ptr && t.Elem().Kind() == reflect.Slice:
+		return &listPtrConverter{t, newSingularConverter(t.Elem().Elem(), fd)}
+	case t.Kind() == reflect.Slice:
+		return &listConverter{t, newSingularConverter(t.Elem(), fd)}
+	}
+	panic(fmt.Sprintf("invalid Go type %v for field %v", t, fd.FullName()))
+}
+
+type listConverter struct {
+	goType reflect.Type // []T
+	c      Converter
+}
+
+func (c *listConverter) PBValueOf(v reflect.Value) pref.Value {
+	if v.Type() != c.goType {
+		panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
+	}
+	pv := reflect.New(c.goType)
+	pv.Elem().Set(v)
+	return pref.ValueOfList(&listReflect{pv, c.c})
+}
+
+func (c *listConverter) GoValueOf(v pref.Value) reflect.Value {
+	rv := v.List().(*listReflect).v
+	if rv.IsNil() {
+		return reflect.Zero(c.goType)
+	}
+	return rv.Elem()
+}
+
+func (c *listConverter) IsValidPB(v pref.Value) bool {
+	list, ok := v.Interface().(*listReflect)
+	if !ok {
+		return false
+	}
+	return list.v.Type().Elem() == c.goType
+}
+
+func (c *listConverter) IsValidGo(v reflect.Value) bool {
+	return v.IsValid() && v.Type() == c.goType
+}
+
+func (c *listConverter) New() pref.Value {
+	return pref.ValueOfList(&listReflect{reflect.New(c.goType), c.c})
+}
+
+func (c *listConverter) Zero() pref.Value {
+	return pref.ValueOfList(&listReflect{reflect.Zero(reflect.PtrTo(c.goType)), c.c})
+}
+
+type listPtrConverter struct {
+	goType reflect.Type // *[]T
+	c      Converter
+}
+
+func (c *listPtrConverter) PBValueOf(v reflect.Value) pref.Value {
+	if v.Type() != c.goType {
+		panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
+	}
+	return pref.ValueOfList(&listReflect{v, c.c})
+}
+
+func (c *listPtrConverter) GoValueOf(v pref.Value) reflect.Value {
+	return v.List().(*listReflect).v
+}
+
+func (c *listPtrConverter) IsValidPB(v pref.Value) bool {
+	list, ok := v.Interface().(*listReflect)
+	if !ok {
+		return false
+	}
+	return list.v.Type() == c.goType
+}
+
+func (c *listPtrConverter) IsValidGo(v reflect.Value) bool {
+	return v.IsValid() && v.Type() == c.goType
+}
+
+func (c *listPtrConverter) New() pref.Value {
+	return c.PBValueOf(reflect.New(c.goType.Elem()))
+}
+
+func (c *listPtrConverter) Zero() pref.Value {
+	return c.PBValueOf(reflect.Zero(c.goType))
+}
+
+type listReflect struct {
+	v    reflect.Value // *[]T
+	conv Converter
+}
+
+func (ls *listReflect) Len() int {
+	if ls.v.IsNil() {
+		return 0
+	}
+	return ls.v.Elem().Len()
+}
+func (ls *listReflect) Get(i int) pref.Value {
+	return ls.conv.PBValueOf(ls.v.Elem().Index(i))
+}
+func (ls *listReflect) Set(i int, v pref.Value) {
+	ls.v.Elem().Index(i).Set(ls.conv.GoValueOf(v))
+}
+func (ls *listReflect) Append(v pref.Value) {
+	ls.v.Elem().Set(reflect.Append(ls.v.Elem(), ls.conv.GoValueOf(v)))
+}
+func (ls *listReflect) AppendMutable() pref.Value {
+	if _, ok := ls.conv.(*messageConverter); !ok {
+		panic("invalid AppendMutable on list with non-message type")
+	}
+	v := ls.NewElement()
+	ls.Append(v)
+	return v
+}
+func (ls *listReflect) Truncate(i int) {
+	ls.v.Elem().Set(ls.v.Elem().Slice(0, i))
+}
+func (ls *listReflect) NewElement() pref.Value {
+	return ls.conv.New()
+}
+func (ls *listReflect) IsValid() bool {
+	return !ls.v.IsNil()
+}
+func (ls *listReflect) protoUnwrap() interface{} {
+	return ls.v.Interface()
+}