Enable stub generation using Hydrogen/Lithium (again)

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h
index 73438d75db2fc74cd86ffea129ab7af953246c51..598be01516c717bc8c31f09c942202bb13b84b42 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -47,6 +47,10 @@ static const int kSizeOfOptimizedStrictModePrologue = 14;
 
 class CodeGenerator: public AstVisitor {
  public:
+  CodeGenerator() {
+    InitializeAstVisitor();
+  }
+
   static bool MakeCode(CompilationInfo* info);
 
   // Printing of AST, etc. as requested by flags.
@@ -66,6 +70,8 @@ class CodeGenerator: public AstVisitor {
                               int pos,
                               bool right_here = false);
 
+  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(CodeGenerator);
 };