Standardize usage of virtual/override/final in sync/

sync/engine/non_blocking_type_commit_contribution.h

Index: sync/engine/non_blocking_type_commit_contribution.h
diff --git a/sync/engine/non_blocking_type_commit_contribution.h b/sync/engine/non_blocking_type_commit_contribution.h
index 5633277ffd40e03333c14bcda82c4a7a2367cbf4..0ee54f03d60e9896b23855d68e3efcffc3f41ee9 100644
--- a/sync/engine/non_blocking_type_commit_contribution.h
+++ b/sync/engine/non_blocking_type_commit_contribution.h
@@ -26,15 +26,15 @@ class NonBlockingTypeCommitContribution : public CommitContribution {
       const google::protobuf::RepeatedPtrField<sync_pb::SyncEntity>& entities,
       const std::vector<int64>& sequence_numbers,
       ModelTypeSyncWorkerImpl* worker);
-  virtual ~NonBlockingTypeCommitContribution();
+  ~NonBlockingTypeCommitContribution() override;
 
   // Implementation of CommitContribution
-  virtual void AddToCommitMessage(sync_pb::ClientToServerMessage* msg) override;
-  virtual SyncerError ProcessCommitResponse(
+  void AddToCommitMessage(sync_pb::ClientToServerMessage* msg) override;
+  SyncerError ProcessCommitResponse(
       const sync_pb::ClientToServerResponse& response,
       sessions::StatusController* status) override;
-  virtual void CleanUp() override;
-  virtual size_t GetNumEntries() const override;
+  void CleanUp() override;
+  size_t GetNumEntries() const override;
 
  private:
   // A non-owned pointer back to the object that created this contribution.