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

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index b33ee0c863d26da882553dd5e7ace770d658c249..a170a71512b4be188be53908868e64c3911325ed 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -138,10 +138,10 @@ class LazyTypeCache FINAL : public ZoneObject {
 };
 
 
-class Typer::Decorator : public GraphDecorator {
+class Typer::Decorator FINAL : public GraphDecorator {
  public:
   explicit Decorator(Typer* typer) : typer_(typer) {}
-  virtual void Decorate(Node* node);
+  void Decorate(Node* node) FINAL;
 
  private:
   Typer* typer_;