sync: add comment to SyncerProtoUtil

sync/engine/syncer_proto_util.h

 // 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.
 
 #ifndef SYNC_ENGINE_SYNCER_PROTO_UTIL_H_
 #define SYNC_ENGINE_SYNCER_PROTO_UTIL_H_
 
 #include <string>
 
 #include "base/gtest_prod_util.h"
@@ skipping 24 matching lines @@
 namespace syncable {
 class Directory;
 class Entry;
 }
 
 class SyncerProtoUtil {
  public:
   // Posts the given message and fills the buffer with the returned value.
   // Returns true on success.  Also handles store birthday verification: will
   // produce a SyncError if the birthday is incorrect.
+  // NOTE: This will add all fields that must be sent on every request, which
+  // includes store birthday, protocol version, client chips, api keys, etc.
   static SyncerError PostClientToServerMessage(
       sync_pb::ClientToServerMessage* msg,
       sync_pb::ClientToServerResponse* response,
       sessions::SyncSession* session);
 
   // Compares a syncable Entry to SyncEntity, returns true iff the data is
   // identical.
   //
   // TODO(sync): The places where this function is used are arguable big causes
   // of the fragility, because there's a tendency to freak out the moment the
@@ skipping 88 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(SyncerProtoUtilTest, VerifyResponseBirthday);
   FRIEND_TEST_ALL_PREFIXES(SyncerProtoUtilTest, HandleThrottlingNoDatatypes);
   FRIEND_TEST_ALL_PREFIXES(SyncerProtoUtilTest, HandleThrottlingWithDatatypes);
 
   DISALLOW_COPY_AND_ASSIGN(SyncerProtoUtil);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_SYNCER_PROTO_UTIL_H_