LogDog: Add collector service implementation.

common/proto/logdog/services/config.proto

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 syntax = "proto3";
 
 package services;
 
 import "transport.proto";
 import "storage.proto";
+import "google/protobuf/duration.proto";
 
 // Config is the overall instance configuration.
 message Config {
   // Configuration for the Pub/Sub instances.
   Transport transport = 10;
   // Configuration for Storage.
   Storage storage = 11;
 
   // Coordinator is the coordinator service configuration.
   Coordinator coordinator = 20;
@@ skipping 13 matching lines @@
   string service_auth_group = 11;
 }
 
 // Collector is the set of configuration parameters for Collector instances.
 message Collector {
   // Workers is the number of ingest workers to run.
   int32 workers = 1;
 
   // The number of transport worker goroutines to run.
   int32 transport_workers = 2;
+
+  // The maximum amount of time that cached stream state is valid.
+  google.protobuf.Duration state_cache_expiration = 3;
 }