diff --git a/vendor/google.golang.org/protobuf/internal/impl/convert_map.go b/vendor/google.golang.org/protobuf/internal/impl/convert_map.go
new file mode 100644
index 0000000..de06b25
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/convert_map.go
@@ -0,0 +1,121 @@
+// 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"
+)
+
+type mapConverter struct {
+	goType           reflect.Type // map[K]V
+	keyConv, valConv Converter
+}
+
+func newMapConverter(t reflect.Type, fd pref.FieldDescriptor) *mapConverter {
+	if t.Kind() != reflect.Map {
+		panic(fmt.Sprintf("invalid Go type %v for field %v", t, fd.FullName()))
+	}
+	return &mapConverter{
+		goType:  t,
+		keyConv: newSingularConverter(t.Key(), fd.MapKey()),
+		valConv: newSingularConverter(t.Elem(), fd.MapValue()),
+	}
+}
+
+func (c *mapConverter) 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.ValueOfMap(&mapReflect{v, c.keyConv, c.valConv})
+}
+
+func (c *mapConverter) GoValueOf(v pref.Value) reflect.Value {
+	return v.Map().(*mapReflect).v
+}
+
+func (c *mapConverter) IsValidPB(v pref.Value) bool {
+	mapv, ok := v.Interface().(*mapReflect)
+	if !ok {
+		return false
+	}
+	return mapv.v.Type() == c.goType
+}
+
+func (c *mapConverter) IsValidGo(v reflect.Value) bool {
+	return v.IsValid() && v.Type() == c.goType
+}
+
+func (c *mapConverter) New() pref.Value {
+	return c.PBValueOf(reflect.MakeMap(c.goType))
+}
+
+func (c *mapConverter) Zero() pref.Value {
+	return c.PBValueOf(reflect.Zero(c.goType))
+}
+
+type mapReflect struct {
+	v       reflect.Value // map[K]V
+	keyConv Converter
+	valConv Converter
+}
+
+func (ms *mapReflect) Len() int {
+	return ms.v.Len()
+}
+func (ms *mapReflect) Has(k pref.MapKey) bool {
+	rk := ms.keyConv.GoValueOf(k.Value())
+	rv := ms.v.MapIndex(rk)
+	return rv.IsValid()
+}
+func (ms *mapReflect) Get(k pref.MapKey) pref.Value {
+	rk := ms.keyConv.GoValueOf(k.Value())
+	rv := ms.v.MapIndex(rk)
+	if !rv.IsValid() {
+		return pref.Value{}
+	}
+	return ms.valConv.PBValueOf(rv)
+}
+func (ms *mapReflect) Set(k pref.MapKey, v pref.Value) {
+	rk := ms.keyConv.GoValueOf(k.Value())
+	rv := ms.valConv.GoValueOf(v)
+	ms.v.SetMapIndex(rk, rv)
+}
+func (ms *mapReflect) Clear(k pref.MapKey) {
+	rk := ms.keyConv.GoValueOf(k.Value())
+	ms.v.SetMapIndex(rk, reflect.Value{})
+}
+func (ms *mapReflect) Mutable(k pref.MapKey) pref.Value {
+	if _, ok := ms.valConv.(*messageConverter); !ok {
+		panic("invalid Mutable on map with non-message value type")
+	}
+	v := ms.Get(k)
+	if !v.IsValid() {
+		v = ms.NewValue()
+		ms.Set(k, v)
+	}
+	return v
+}
+func (ms *mapReflect) Range(f func(pref.MapKey, pref.Value) bool) {
+	iter := mapRange(ms.v)
+	for iter.Next() {
+		k := ms.keyConv.PBValueOf(iter.Key()).MapKey()
+		v := ms.valConv.PBValueOf(iter.Value())
+		if !f(k, v) {
+			return
+		}
+	}
+}
+func (ms *mapReflect) NewValue() pref.Value {
+	return ms.valConv.New()
+}
+func (ms *mapReflect) IsValid() bool {
+	return !ms.v.IsNil()
+}
+func (ms *mapReflect) protoUnwrap() interface{} {
+	return ms.v.Interface()
+}