Allocate script scopes using a separate constructor

src/ast/scopes.h

Index: src/ast/scopes.h
diff --git a/src/ast/scopes.h b/src/ast/scopes.h
index 708d6dde75e7c8065dd6ead456841fbf339873a1..d88a0699bc08f708995dd0afbbc7ca39173913bb 100644
--- a/src/ast/scopes.h
+++ b/src/ast/scopes.h
@@ -446,6 +446,9 @@ class Scope: public ZoneObject {
   void set_is_debug_evaluate_scope() { is_debug_evaluate_scope_ = true; }
 
  protected:
+  // Creates a script scope.
+  explicit Scope(Zone* zone);
+
   void set_language_mode(LanguageMode language_mode) {
     is_strict_ = is_strict(language_mode);
   }
@@ -662,6 +665,8 @@ class DeclarationScope : public Scope {
                    FunctionKind function_kind = kNormalFunction);
   DeclarationScope(Zone* zone, Scope* inner_scope, ScopeType scope_type,
                    Handle<ScopeInfo> scope_info);
+  // Creates a script scope.
+  explicit DeclarationScope(Zone* zone);
 
   bool IsDeclaredParameter(const AstRawString* name) {
     // If IsSimpleParameterList is false, duplicate parameters are not allowed,