diff --git a/go/vendor/google.golang.org/grpc/balancer_conn_wrappers.go b/go/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
new file mode 100644
index 0000000..1ab95fd
--- /dev/null
+++ b/go/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
@@ -0,0 +1,301 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"fmt"
+	"sync"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/resolver"
+)
+
+// scStateUpdate contains the subConn and the new state it changed to.
+type scStateUpdate struct {
+	sc    balancer.SubConn
+	state connectivity.State
+}
+
+// scStateUpdateBuffer is an unbounded channel for scStateChangeTuple.
+// TODO make a general purpose buffer that uses interface{}.
+type scStateUpdateBuffer struct {
+	c       chan *scStateUpdate
+	mu      sync.Mutex
+	backlog []*scStateUpdate
+}
+
+func newSCStateUpdateBuffer() *scStateUpdateBuffer {
+	return &scStateUpdateBuffer{
+		c: make(chan *scStateUpdate, 1),
+	}
+}
+
+func (b *scStateUpdateBuffer) put(t *scStateUpdate) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if len(b.backlog) == 0 {
+		select {
+		case b.c <- t:
+			return
+		default:
+		}
+	}
+	b.backlog = append(b.backlog, t)
+}
+
+func (b *scStateUpdateBuffer) load() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if len(b.backlog) > 0 {
+		select {
+		case b.c <- b.backlog[0]:
+			b.backlog[0] = nil
+			b.backlog = b.backlog[1:]
+		default:
+		}
+	}
+}
+
+// get returns the channel that the scStateUpdate will be sent to.
+//
+// Upon receiving, the caller should call load to send another
+// scStateChangeTuple onto the channel if there is any.
+func (b *scStateUpdateBuffer) get() <-chan *scStateUpdate {
+	return b.c
+}
+
+// resolverUpdate contains the new resolved addresses or error if there's
+// any.
+type resolverUpdate struct {
+	addrs []resolver.Address
+	err   error
+}
+
+// ccBalancerWrapper is a wrapper on top of cc for balancers.
+// It implements balancer.ClientConn interface.
+type ccBalancerWrapper struct {
+	cc               *ClientConn
+	balancer         balancer.Balancer
+	stateChangeQueue *scStateUpdateBuffer
+	resolverUpdateCh chan *resolverUpdate
+	done             chan struct{}
+
+	mu       sync.Mutex
+	subConns map[*acBalancerWrapper]struct{}
+}
+
+func newCCBalancerWrapper(cc *ClientConn, b balancer.Builder, bopts balancer.BuildOptions) *ccBalancerWrapper {
+	ccb := &ccBalancerWrapper{
+		cc:               cc,
+		stateChangeQueue: newSCStateUpdateBuffer(),
+		resolverUpdateCh: make(chan *resolverUpdate, 1),
+		done:             make(chan struct{}),
+		subConns:         make(map[*acBalancerWrapper]struct{}),
+	}
+	go ccb.watcher()
+	ccb.balancer = b.Build(ccb, bopts)
+	return ccb
+}
+
+// watcher balancer functions sequentially, so the balancer can be implemented
+// lock-free.
+func (ccb *ccBalancerWrapper) watcher() {
+	for {
+		select {
+		case t := <-ccb.stateChangeQueue.get():
+			ccb.stateChangeQueue.load()
+			select {
+			case <-ccb.done:
+				ccb.balancer.Close()
+				return
+			default:
+			}
+			ccb.balancer.HandleSubConnStateChange(t.sc, t.state)
+		case t := <-ccb.resolverUpdateCh:
+			select {
+			case <-ccb.done:
+				ccb.balancer.Close()
+				return
+			default:
+			}
+			ccb.balancer.HandleResolvedAddrs(t.addrs, t.err)
+		case <-ccb.done:
+		}
+
+		select {
+		case <-ccb.done:
+			ccb.balancer.Close()
+			ccb.mu.Lock()
+			scs := ccb.subConns
+			ccb.subConns = nil
+			ccb.mu.Unlock()
+			for acbw := range scs {
+				ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
+			}
+			return
+		default:
+		}
+	}
+}
+
+func (ccb *ccBalancerWrapper) close() {
+	close(ccb.done)
+}
+
+func (ccb *ccBalancerWrapper) handleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
+	// When updating addresses for a SubConn, if the address in use is not in
+	// the new addresses, the old ac will be tearDown() and a new ac will be
+	// created. tearDown() generates a state change with Shutdown state, we
+	// don't want the balancer to receive this state change. So before
+	// tearDown() on the old ac, ac.acbw (acWrapper) will be set to nil, and
+	// this function will be called with (nil, Shutdown). We don't need to call
+	// balancer method in this case.
+	if sc == nil {
+		return
+	}
+	ccb.stateChangeQueue.put(&scStateUpdate{
+		sc:    sc,
+		state: s,
+	})
+}
+
+func (ccb *ccBalancerWrapper) handleResolvedAddrs(addrs []resolver.Address, err error) {
+	select {
+	case <-ccb.resolverUpdateCh:
+	default:
+	}
+	ccb.resolverUpdateCh <- &resolverUpdate{
+		addrs: addrs,
+		err:   err,
+	}
+}
+
+func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
+	if len(addrs) <= 0 {
+		return nil, fmt.Errorf("grpc: cannot create SubConn with empty address list")
+	}
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return nil, fmt.Errorf("grpc: ClientConn balancer wrapper was closed")
+	}
+	ac, err := ccb.cc.newAddrConn(addrs, opts)
+	if err != nil {
+		return nil, err
+	}
+	acbw := &acBalancerWrapper{ac: ac}
+	acbw.ac.mu.Lock()
+	ac.acbw = acbw
+	acbw.ac.mu.Unlock()
+	ccb.subConns[acbw] = struct{}{}
+	return acbw, nil
+}
+
+func (ccb *ccBalancerWrapper) RemoveSubConn(sc balancer.SubConn) {
+	acbw, ok := sc.(*acBalancerWrapper)
+	if !ok {
+		return
+	}
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return
+	}
+	delete(ccb.subConns, acbw)
+	ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
+}
+
+func (ccb *ccBalancerWrapper) UpdateBalancerState(s connectivity.State, p balancer.Picker) {
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	if ccb.subConns == nil {
+		return
+	}
+	ccb.cc.csMgr.updateState(s)
+	ccb.cc.blockingpicker.updatePicker(p)
+}
+
+func (ccb *ccBalancerWrapper) ResolveNow(o resolver.ResolveNowOption) {
+	ccb.cc.resolveNow(o)
+}
+
+func (ccb *ccBalancerWrapper) Target() string {
+	return ccb.cc.target
+}
+
+// acBalancerWrapper is a wrapper on top of ac for balancers.
+// It implements balancer.SubConn interface.
+type acBalancerWrapper struct {
+	mu sync.Mutex
+	ac *addrConn
+}
+
+func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
+	acbw.mu.Lock()
+	defer acbw.mu.Unlock()
+	if len(addrs) <= 0 {
+		acbw.ac.tearDown(errConnDrain)
+		return
+	}
+	if !acbw.ac.tryUpdateAddrs(addrs) {
+		cc := acbw.ac.cc
+		opts := acbw.ac.scopts
+		acbw.ac.mu.Lock()
+		// Set old ac.acbw to nil so the Shutdown state update will be ignored
+		// by balancer.
+		//
+		// TODO(bar) the state transition could be wrong when tearDown() old ac
+		// and creating new ac, fix the transition.
+		acbw.ac.acbw = nil
+		acbw.ac.mu.Unlock()
+		acState := acbw.ac.getState()
+		acbw.ac.tearDown(errConnDrain)
+
+		if acState == connectivity.Shutdown {
+			return
+		}
+
+		ac, err := cc.newAddrConn(addrs, opts)
+		if err != nil {
+			grpclog.Warningf("acBalancerWrapper: UpdateAddresses: failed to newAddrConn: %v", err)
+			return
+		}
+		acbw.ac = ac
+		ac.mu.Lock()
+		ac.acbw = acbw
+		ac.mu.Unlock()
+		if acState != connectivity.Idle {
+			ac.connect()
+		}
+	}
+}
+
+func (acbw *acBalancerWrapper) Connect() {
+	acbw.mu.Lock()
+	defer acbw.mu.Unlock()
+	acbw.ac.connect()
+}
+
+func (acbw *acBalancerWrapper) getAddrConn() *addrConn {
+	acbw.mu.Lock()
+	defer acbw.mu.Unlock()
+	return acbw.ac
+}