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 d4440952135d93a0bf7d72df2fd7e92ebbe6bc3f..3a7646bd1bb7ff68b959509f6a6acacf02fadd9e 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -44,6 +44,10 @@ enum TypeofState { INSIDE_TYPEOF, NOT_INSIDE_TYPEOF };
 
 class CodeGenerator: public AstVisitor {
  public:
+  CodeGenerator() {
+    InitializeAstVisitor();
+  }
+
   static bool MakeCode(CompilationInfo* info);
 
   // Printing of AST, etc. as requested by flags.
@@ -63,6 +67,8 @@ class CodeGenerator: public AstVisitor {
                               int pos,
                               bool right_here = false);
 
+  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(CodeGenerator);
 };