Reuse AstValueFactory when optimizing.

src/compiler.h

Index: src/compiler.h
diff --git a/src/compiler.h b/src/compiler.h
index 9d91b21bd3d4851b9141ebbd0b145a23087a82ac..fdb79005085ed89dd97b2d0369cf52ba5eca8b67 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -323,8 +323,10 @@ class CompilationInfo {
   int optimization_id() const { return optimization_id_; }
 
   AstValueFactory* ast_value_factory() const { return ast_value_factory_; }
-  void SetAstValueFactory(AstValueFactory* ast_value_factory) {
+  void SetAstValueFactory(AstValueFactory* ast_value_factory,
+                          bool owned = true) {
     ast_value_factory_ = ast_value_factory;
+    ast_value_factory_owned_ = owned;
   }
 
  protected:
@@ -471,6 +473,7 @@ class CompilationInfo {
   int optimization_id_;
 
   AstValueFactory* ast_value_factory_;
+  bool ast_value_factory_owned_;
 
   DISALLOW_COPY_AND_ASSIGN(CompilationInfo);
 };