Rewind zonelists in scopes when resetting rather than clearing

src/ast/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/ast/ast.h"
@@ skipping 1177 matching lines @@
     non_locals = StringSet::Add(non_locals, proxy->name());
   }
   return non_locals;
 }
 
 void DeclarationScope::ResetAfterPreparsing(AstValueFactory* ast_value_factory,
                                             bool aborted) {
   DCHECK(is_function_scope());
 
   // Reset all non-trivial members.
-  decls_.Clear();
-  locals_.Clear();
+  decls_.Rewind(0);
+  locals_.Rewind(0);
   sloppy_block_function_map_.Clear();
   variables_.Clear();
   // Make sure we won't walk the scope tree from here on.
   inner_scope_ = nullptr;
   unresolved_ = nullptr;
 
   // TODO(verwaest): We should properly preparse the parameters (no declarations
   // should be created), and reparse on abort.
   if (aborted) {
     if (!IsArrowFunction(function_kind_)) {
       DeclareDefaultFunctionVariables(ast_value_factory);
     }
     // Recreate declarations for parameters.
     for (int i = 0; i < params_.length(); i++) {
       Variable* var = params_[i];
       if (var->mode() == TEMPORARY) {
         locals_.Add(var, zone());
       } else if (variables_.Lookup(var->raw_name()) == nullptr) {
         variables_.Add(zone(), var);
         locals_.Add(var, zone());
       }
     }
   } else {
-    params_.Clear();
+    params_.Rewind(0);
   }
 
 #ifdef DEBUG
   needs_migration_ = false;
 #endif
 
   is_lazily_parsed_ = !aborted;
 }
 
 void DeclarationScope::AnalyzePartially(AstNodeFactory* ast_node_factory) {
@@ skipping 670 matching lines @@
   Variable* function =
       is_function_scope() ? AsDeclarationScope()->function_var() : nullptr;
   bool is_function_var_in_context =
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
          (is_function_var_in_context ? 1 : 0);
 }
 
 }  // namespace internal
 }  // namespace v8