[turbofan] Cleanup use of virtual, OVERRIDE, FINAL.

src/compiler/source-position.cc

Index: src/compiler/source-position.cc
diff --git a/src/compiler/source-position.cc b/src/compiler/source-position.cc
index 9503010fd4b091762e888bfc20de4a9be82340aa..9e21ae415a6eaa512d32a776b3d492597cb25218 100644
--- a/src/compiler/source-position.cc
+++ b/src/compiler/source-position.cc
@@ -10,12 +10,12 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-class SourcePositionTable::Decorator : public GraphDecorator {
+class SourcePositionTable::Decorator FINAL : public GraphDecorator {
  public:
   explicit Decorator(SourcePositionTable* source_positions)
       : source_positions_(source_positions) {}
 
-  virtual void Decorate(Node* node) {
+  void Decorate(Node* node) FINAL {
     DCHECK(!source_positions_->current_position_.IsInvalid());
     source_positions_->table_.Set(node, source_positions_->current_position_);
   }