diff --git a/vendor/google.golang.org/protobuf/proto/merge.go b/vendor/google.golang.org/protobuf/proto/merge.go
new file mode 100644
index 0000000..d761ab3
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/proto/merge.go
@@ -0,0 +1,139 @@
+// 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 proto
+
+import (
+	"fmt"
+
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/runtime/protoiface"
+)
+
+// Merge merges src into dst, which must be a message with the same descriptor.
+//
+// Populated scalar fields in src are copied to dst, while populated
+// singular messages in src are merged into dst by recursively calling Merge.
+// The elements of every list field in src is appended to the corresponded
+// list fields in dst. The entries of every map field in src is copied into
+// the corresponding map field in dst, possibly replacing existing entries.
+// The unknown fields of src are appended to the unknown fields of dst.
+//
+// It is semantically equivalent to unmarshaling the encoded form of src
+// into dst with the UnmarshalOptions.Merge option specified.
+func Merge(dst, src Message) {
+	// TODO: Should nil src be treated as semantically equivalent to a
+	// untyped, read-only, empty message? What about a nil dst?
+
+	dstMsg, srcMsg := dst.ProtoReflect(), src.ProtoReflect()
+	if dstMsg.Descriptor() != srcMsg.Descriptor() {
+		if got, want := dstMsg.Descriptor().FullName(), srcMsg.Descriptor().FullName(); got != want {
+			panic(fmt.Sprintf("descriptor mismatch: %v != %v", got, want))
+		}
+		panic("descriptor mismatch")
+	}
+	mergeOptions{}.mergeMessage(dstMsg, srcMsg)
+}
+
+// Clone returns a deep copy of m.
+// If the top-level message is invalid, it returns an invalid message as well.
+func Clone(m Message) Message {
+	// NOTE: Most usages of Clone assume the following properties:
+	//	t := reflect.TypeOf(m)
+	//	t == reflect.TypeOf(m.ProtoReflect().New().Interface())
+	//	t == reflect.TypeOf(m.ProtoReflect().Type().Zero().Interface())
+	//
+	// Embedding protobuf messages breaks this since the parent type will have
+	// a forwarded ProtoReflect method, but the Interface method will return
+	// the underlying embedded message type.
+	if m == nil {
+		return nil
+	}
+	src := m.ProtoReflect()
+	if !src.IsValid() {
+		return src.Type().Zero().Interface()
+	}
+	dst := src.New()
+	mergeOptions{}.mergeMessage(dst, src)
+	return dst.Interface()
+}
+
+// mergeOptions provides a namespace for merge functions, and can be
+// exported in the future if we add user-visible merge options.
+type mergeOptions struct{}
+
+func (o mergeOptions) mergeMessage(dst, src protoreflect.Message) {
+	methods := protoMethods(dst)
+	if methods != nil && methods.Merge != nil {
+		in := protoiface.MergeInput{
+			Destination: dst,
+			Source:      src,
+		}
+		out := methods.Merge(in)
+		if out.Flags&protoiface.MergeComplete != 0 {
+			return
+		}
+	}
+
+	if !dst.IsValid() {
+		panic(fmt.Sprintf("cannot merge into invalid %v message", dst.Descriptor().FullName()))
+	}
+
+	src.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
+		switch {
+		case fd.IsList():
+			o.mergeList(dst.Mutable(fd).List(), v.List(), fd)
+		case fd.IsMap():
+			o.mergeMap(dst.Mutable(fd).Map(), v.Map(), fd.MapValue())
+		case fd.Message() != nil:
+			o.mergeMessage(dst.Mutable(fd).Message(), v.Message())
+		case fd.Kind() == protoreflect.BytesKind:
+			dst.Set(fd, o.cloneBytes(v))
+		default:
+			dst.Set(fd, v)
+		}
+		return true
+	})
+
+	if len(src.GetUnknown()) > 0 {
+		dst.SetUnknown(append(dst.GetUnknown(), src.GetUnknown()...))
+	}
+}
+
+func (o mergeOptions) mergeList(dst, src protoreflect.List, fd protoreflect.FieldDescriptor) {
+	// Merge semantics appends to the end of the existing list.
+	for i, n := 0, src.Len(); i < n; i++ {
+		switch v := src.Get(i); {
+		case fd.Message() != nil:
+			dstv := dst.NewElement()
+			o.mergeMessage(dstv.Message(), v.Message())
+			dst.Append(dstv)
+		case fd.Kind() == protoreflect.BytesKind:
+			dst.Append(o.cloneBytes(v))
+		default:
+			dst.Append(v)
+		}
+	}
+}
+
+func (o mergeOptions) mergeMap(dst, src protoreflect.Map, fd protoreflect.FieldDescriptor) {
+	// Merge semantics replaces, rather than merges into existing entries.
+	src.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
+		switch {
+		case fd.Message() != nil:
+			dstv := dst.NewValue()
+			o.mergeMessage(dstv.Message(), v.Message())
+			dst.Set(k, dstv)
+		case fd.Kind() == protoreflect.BytesKind:
+			dst.Set(k, o.cloneBytes(v))
+		default:
+			dst.Set(k, v)
+		}
+		return true
+	})
+}
+
+func (o mergeOptions) cloneBytes(v protoreflect.Value) protoreflect.Value {
+	return protoreflect.ValueOfBytes(append([]byte{}, v.Bytes()...))
+}