diff --git a/vendor/google.golang.org/protobuf/internal/impl/extension.go b/vendor/google.golang.org/protobuf/internal/impl/extension.go
new file mode 100644
index 0000000..e904fd9
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/extension.go
@@ -0,0 +1,156 @@
+// 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 (
+	"reflect"
+	"sync"
+	"sync/atomic"
+
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+	piface "google.golang.org/protobuf/runtime/protoiface"
+)
+
+// ExtensionInfo implements ExtensionType.
+//
+// This type contains a number of exported fields for legacy compatibility.
+// The only non-deprecated use of this type is through the methods of the
+// ExtensionType interface.
+type ExtensionInfo struct {
+	// An ExtensionInfo may exist in several stages of initialization.
+	//
+	// extensionInfoUninitialized: Some or all of the legacy exported
+	// fields may be set, but none of the unexported fields have been
+	// initialized. This is the starting state for an ExtensionInfo
+	// in legacy generated code.
+	//
+	// extensionInfoDescInit: The desc field is set, but other unexported fields
+	// may not be initialized. Legacy exported fields may or may not be set.
+	// This is the starting state for an ExtensionInfo in newly generated code.
+	//
+	// extensionInfoFullInit: The ExtensionInfo is fully initialized.
+	// This state is only entered after lazy initialization is complete.
+	init uint32
+	mu   sync.Mutex
+
+	goType reflect.Type
+	desc   extensionTypeDescriptor
+	conv   Converter
+	info   *extensionFieldInfo // for fast-path method implementations
+
+	// ExtendedType is a typed nil-pointer to the parent message type that
+	// is being extended. It is possible for this to be unpopulated in v2
+	// since the message may no longer implement the MessageV1 interface.
+	//
+	// Deprecated: Use the ExtendedType method instead.
+	ExtendedType piface.MessageV1
+
+	// ExtensionType is the zero value of the extension type.
+	//
+	// For historical reasons, reflect.TypeOf(ExtensionType) and the
+	// type returned by InterfaceOf may not be identical.
+	//
+	// Deprecated: Use InterfaceOf(xt.Zero()) instead.
+	ExtensionType interface{}
+
+	// Field is the field number of the extension.
+	//
+	// Deprecated: Use the Descriptor().Number method instead.
+	Field int32
+
+	// Name is the fully qualified name of extension.
+	//
+	// Deprecated: Use the Descriptor().FullName method instead.
+	Name string
+
+	// Tag is the protobuf struct tag used in the v1 API.
+	//
+	// Deprecated: Do not use.
+	Tag string
+
+	// Filename is the proto filename in which the extension is defined.
+	//
+	// Deprecated: Use Descriptor().ParentFile().Path() instead.
+	Filename string
+}
+
+// Stages of initialization: See the ExtensionInfo.init field.
+const (
+	extensionInfoUninitialized = 0
+	extensionInfoDescInit      = 1
+	extensionInfoFullInit      = 2
+)
+
+func InitExtensionInfo(xi *ExtensionInfo, xd pref.ExtensionDescriptor, goType reflect.Type) {
+	xi.goType = goType
+	xi.desc = extensionTypeDescriptor{xd, xi}
+	xi.init = extensionInfoDescInit
+}
+
+func (xi *ExtensionInfo) New() pref.Value {
+	return xi.lazyInit().New()
+}
+func (xi *ExtensionInfo) Zero() pref.Value {
+	return xi.lazyInit().Zero()
+}
+func (xi *ExtensionInfo) ValueOf(v interface{}) pref.Value {
+	return xi.lazyInit().PBValueOf(reflect.ValueOf(v))
+}
+func (xi *ExtensionInfo) InterfaceOf(v pref.Value) interface{} {
+	return xi.lazyInit().GoValueOf(v).Interface()
+}
+func (xi *ExtensionInfo) IsValidValue(v pref.Value) bool {
+	return xi.lazyInit().IsValidPB(v)
+}
+func (xi *ExtensionInfo) IsValidInterface(v interface{}) bool {
+	return xi.lazyInit().IsValidGo(reflect.ValueOf(v))
+}
+func (xi *ExtensionInfo) TypeDescriptor() pref.ExtensionTypeDescriptor {
+	if atomic.LoadUint32(&xi.init) < extensionInfoDescInit {
+		xi.lazyInitSlow()
+	}
+	return &xi.desc
+}
+
+func (xi *ExtensionInfo) lazyInit() Converter {
+	if atomic.LoadUint32(&xi.init) < extensionInfoFullInit {
+		xi.lazyInitSlow()
+	}
+	return xi.conv
+}
+
+func (xi *ExtensionInfo) lazyInitSlow() {
+	xi.mu.Lock()
+	defer xi.mu.Unlock()
+
+	if xi.init == extensionInfoFullInit {
+		return
+	}
+	defer atomic.StoreUint32(&xi.init, extensionInfoFullInit)
+
+	if xi.desc.ExtensionDescriptor == nil {
+		xi.initFromLegacy()
+	}
+	if !xi.desc.ExtensionDescriptor.IsPlaceholder() {
+		if xi.ExtensionType == nil {
+			xi.initToLegacy()
+		}
+		xi.conv = NewConverter(xi.goType, xi.desc.ExtensionDescriptor)
+		xi.info = makeExtensionFieldInfo(xi.desc.ExtensionDescriptor)
+		xi.info.validation = newValidationInfo(xi.desc.ExtensionDescriptor, xi.goType)
+	}
+}
+
+type extensionTypeDescriptor struct {
+	pref.ExtensionDescriptor
+	xi *ExtensionInfo
+}
+
+func (xtd *extensionTypeDescriptor) Type() pref.ExtensionType {
+	return xtd.xi
+}
+func (xtd *extensionTypeDescriptor) Descriptor() pref.ExtensionDescriptor {
+	return xtd.ExtensionDescriptor
+}