[Sync] Add two more USS integration tests.

components/sync/engine_impl/worker_entity_tracker.cc

Index: components/sync/engine_impl/worker_entity_tracker.cc
diff --git a/components/sync/engine_impl/worker_entity_tracker.cc b/components/sync/engine_impl/worker_entity_tracker.cc
index 4177b2b942034312f60f78c9df10971faa321777..5d18a0cc1cf6bd9d6a873026b3afa3d4951e935c 100644
--- a/components/sync/engine_impl/worker_entity_tracker.cc
+++ b/components/sync/engine_impl/worker_entity_tracker.cc
@@ -125,11 +125,12 @@ void WorkerEntityTracker::ReceiveCommitResponse(CommitResponseData* ack) {
   ClearPendingCommit();
 }
 
-void WorkerEntityTracker::ReceiveUpdate(int64_t version) {
-  if (version <= highest_gu_response_version_)
+void WorkerEntityTracker::ReceiveUpdate(const UpdateResponseData& update) {
+  if (update.response_version <= highest_gu_response_version_)
     return;
 
-  highest_gu_response_version_ = version;
+  highest_gu_response_version_ = update.response_version;
+  id_ = update.entity->id;

[pavely, 2016/09/16 16:11:08]

Could you adjust comment for entities_ in model_type_worker.h to mention that
the map is keyed by client tag hash. This way it will be easier to verify that
adjusting id_ will not break mapping. Also we could make
WorkerEntityTracker::client_tag_hash_ const, this way attempt to modify it will
cause compiler error.

[maxbogue, 2016/09/16 17:39:43]

Done and done.

 
   // Got an applicable update newer than any pending updates.  It must be safe
   // to discard the old encrypted update, if there was one.