diff --git a/vendor/google.golang.org/protobuf/internal/impl/weak.go b/vendor/google.golang.org/protobuf/internal/impl/weak.go
new file mode 100644
index 0000000..009cbef
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/weak.go
@@ -0,0 +1,74 @@
+// Copyright 2019 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"
+
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
+)
+
+// weakFields adds methods to the exported WeakFields type for internal use.
+//
+// The exported type is an alias to an unnamed type, so methods can't be
+// defined directly on it.
+type weakFields WeakFields
+
+func (w weakFields) get(num pref.FieldNumber) (pref.ProtoMessage, bool) {
+	m, ok := w[int32(num)]
+	return m, ok
+}
+
+func (w *weakFields) set(num pref.FieldNumber, m pref.ProtoMessage) {
+	if *w == nil {
+		*w = make(weakFields)
+	}
+	(*w)[int32(num)] = m
+}
+
+func (w *weakFields) clear(num pref.FieldNumber) {
+	delete(*w, int32(num))
+}
+
+func (Export) HasWeak(w WeakFields, num pref.FieldNumber) bool {
+	_, ok := w[int32(num)]
+	return ok
+}
+
+func (Export) ClearWeak(w *WeakFields, num pref.FieldNumber) {
+	delete(*w, int32(num))
+}
+
+func (Export) GetWeak(w WeakFields, num pref.FieldNumber, name pref.FullName) pref.ProtoMessage {
+	if m, ok := w[int32(num)]; ok {
+		return m
+	}
+	mt, _ := protoregistry.GlobalTypes.FindMessageByName(name)
+	if mt == nil {
+		panic(fmt.Sprintf("message %v for weak field is not linked in", name))
+	}
+	return mt.Zero().Interface()
+}
+
+func (Export) SetWeak(w *WeakFields, num pref.FieldNumber, name pref.FullName, m pref.ProtoMessage) {
+	if m != nil {
+		mt, _ := protoregistry.GlobalTypes.FindMessageByName(name)
+		if mt == nil {
+			panic(fmt.Sprintf("message %v for weak field is not linked in", name))
+		}
+		if mt != m.ProtoReflect().Type() {
+			panic(fmt.Sprintf("invalid message type for weak field: got %T, want %T", m, mt.Zero().Interface()))
+		}
+	}
+	if m == nil || !m.ProtoReflect().IsValid() {
+		delete(*w, int32(num))
+		return
+	}
+	if *w == nil {
+		*w = make(weakFields)
+	}
+	(*w)[int32(num)] = m
+}