Revert of Migrate tsmon protos to proto3

common/tsmon/context.go

Index: common/tsmon/context.go
diff --git a/common/tsmon/context.go b/common/tsmon/context.go
index 08fd4fbedadfda7bfa4194c736b13b3fb84f1e2c..55a1b50fd0a0712d7afeda1b30f918c21c62087c 100644
--- a/common/tsmon/context.go
+++ b/common/tsmon/context.go
@@ -7,6 +7,7 @@
 import (
 	"sync"
 
+	"github.com/golang/protobuf/proto"
 	"golang.org/x/net/context"
 
 	"github.com/luci/luci-go/common/tsmon/monitor"
@@ -66,7 +67,7 @@
 // WithDummyInMemory returns a new context holding a new State with a new in-
 // memory store and a fake monitor.
 func WithDummyInMemory(c context.Context) (context.Context, *monitor.Fake) {
-	s := store.NewInMemory(&target.Task{})
+	s := store.NewInMemory(&target.Task{ServiceName: proto.String("")})
 	m := &monitor.Fake{}
 	return WithState(c, &State{
 		S:                 s,