sync: Report GetUpdate triggers to the server

sync/protocol/client_commands.proto

 // Copyright (c) 2012 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.
 //
 // Sync protocol for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 10 matching lines @@
 
   optional int32 max_commit_batch_size = 3;
 
   // Number of seconds to delay between a sessions
   // action and sending a commit message to the
   // server
   optional int32 sessions_commit_delay_seconds = 4;
 
   // Number of seconds to delay before the throttled client should retry.
   optional int32 throttle_delay_seconds = 5;
+
+  // Maximum number of local nudges to buffer per-type.
+  optional int32 client_invalidation_hint_buffer_size = 6;
 };