Implement new invalidations ack tracking system

sync/internal_api/public/base/invalidation.cc

 // Copyright 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.
 
 #include "sync/internal_api/public/base/invalidation.h"
 
 #include <cstddef>
 
 #include "base/json/json_string_value_serializer.h"
 #include "base/rand_util.h"
@@ skipping 93 matching lines @@
 
 const std::string& Invalidation::payload() const {
   DCHECK(!is_unknown_version_);
   return payload_;
 }
 
 const AckHandle& Invalidation::ack_handle() const {
   return ack_handle_;
 }
 
-void Invalidation::set_ack_handle(const AckHandle& ack_handle) {
-  ack_handle_ = ack_handle;
-}
-
 void Invalidation::set_ack_handler(syncer::WeakHandle<AckHandler> handler) {
   ack_handler_ = handler;

[tim (not reviewing), 2013/11/20 18:27:04]

At the very least, this shouldn't ever change from a non-null value to a
different non-null value, correct?  A dcheck would be a good idea.  Might
consider renaming to InitAckHandler(...), but you don't have to.. up to you.

[rlarocque, 2013/11/21 20:09:27]

Done.

 }
 
 bool Invalidation::SupportsAcknowledgement() const {
   return ack_handler_.IsInitialized();
 }
 
 void Invalidation::Acknowledge() const {
   if (SupportsAcknowledgement()) {
     ack_handler_.Call(FROM_HERE,
                       &AckHandler::Acknowledge,
                       id_,
                       ack_handle_);
   }
 }
 
 void Invalidation::Drop(DroppedInvalidationTracker* tracker) const {
   DCHECK(tracker->object_id() == object_id());
   tracker->RecordDropEvent(ack_handler_, ack_handle_);
-  ack_handler_.Call(FROM_HERE,
-                    &AckHandler::Drop,
-                    id_,
-                    ack_handle_);
+  if (SupportsAcknowledgement()) {
+    ack_handler_.Call(FROM_HERE,
+                      &AckHandler::Drop,
+                      id_,
+                      ack_handle_);
+  }
 }
 
 bool Invalidation::Equals(const Invalidation& other) const {
   return id_ == other.id_
       && is_unknown_version_ == other.is_unknown_version_
       && version_ == other.version_
       && payload_ == other.payload_;
 }
 
 scoped_ptr<base::DictionaryValue> Invalidation::ToValue() const {
@@ skipping 23 matching lines @@
     int64 version,
     const std::string& payload,
     AckHandle ack_handle)
   : id_(id),
     is_unknown_version_(is_unknown_version),
     version_(version),
     payload_(payload),
     ack_handle_(ack_handle) {}
 
 }  // namespace syncer