[Sync] ModelTypeWorker should delete tracker for entity deleted on the server

components/sync/engine_impl/worker_entity_tracker.h

Index: components/sync/engine_impl/worker_entity_tracker.h
diff --git a/components/sync/engine_impl/worker_entity_tracker.h b/components/sync/engine_impl/worker_entity_tracker.h
index 3b1bde1b0dba529015b35a8e6852b0b9959f91bd..d95fdc2a35d62bc3bc4e5d3bb86e92032b93ae6e 100644
--- a/components/sync/engine_impl/worker_entity_tracker.h
+++ b/components/sync/engine_impl/worker_entity_tracker.h
@@ -40,6 +40,9 @@ class WorkerEntityTracker {
   // Returns true if this entity should be commited to the server.
   bool HasPendingCommit() const;
 
+  // Returns true if pending commit contains deleted entity.
+  bool IsTombstone() const;

[maxbogue, 2017/01/09 19:44:48]

nit: I'd prefer PendingCommitIsTombstone or PendingCommitIsDeletion. That makes
it clearer that the method is only valid to call if HasPendingCommit is true.

+
   // Populates a sync_pb::SyncEntity for a commit.
   void PopulateCommitProto(sync_pb::SyncEntity* commit_entity) const;