Fix bug with re-scoping arrow function parameter initializers

src/ast/scopes.h

 // 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.
 
 #ifndef V8_AST_SCOPES_H_
 #define V8_AST_SCOPES_H_
 
 #include "src/ast/ast.h"
 #include "src/base/hashmap.h"
 #include "src/pending-compilation-error-handler.h"
@@ skipping 198 matching lines @@
 
   // Remove a temporary variable. This is for adjusting the scope of
   // temporaries used when desugaring parameter initializers.
   // Returns the index at which it was found in this scope, or -1 if
   // it was not found.
   int RemoveTemporary(Variable* var);
 
   // Adds a temporary variable in this scope's TemporaryScope. This is for
   // adjusting the scope of temporaries used when desugaring parameter
   // initializers.
-  void AddTemporary(Variable* var) { temps_.Add(var, zone()); }
+  void AddTemporary(Variable* var) {
+    // Temporaries are only placed in ClosureScopes.
+    DCHECK_EQ(ClosureScope(), this);
+    temps_.Add(var, zone());
+  }
 
   // Adds the specific declaration node to the list of declarations in
   // this scope. The declarations are processed as part of entering
   // the scope; see codegen.cc:ProcessDeclarations.
   void AddDeclaration(Declaration* declaration);
 
   // ---------------------------------------------------------------------------
   // Illegal redeclaration support.
 
   // Check if the scope has conflicting var
@@ skipping 584 matching lines @@
   AstValueFactory* ast_value_factory_;
   Zone* zone_;
 
   PendingCompilationErrorHandler pending_error_handler_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_SCOPES_H_