Simply use the variable index to put them into the right ScopeInfo slot rather than sorting

src/ast/variables.h

 // Copyright 2011 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_VARIABLES_H_
 #define V8_AST_VARIABLES_H_
 
 #include "src/ast/ast-value-factory.h"
 #include "src/zone.h"
 
@@ skipping 84 matching lines @@
   InitializationFlag initialization_flag() const {
     return initialization_flag_;
   }
 
   void AllocateTo(VariableLocation location, int index) {
     DCHECK(IsUnallocated() || (location_ == location && index_ == index));
     location_ = location;
     index_ = index;
   }
 
-  static int CompareIndex(Variable* const* v, Variable* const* w);
-
  private:
   Scope* scope_;
   const AstRawString* name_;
   VariableMode mode_;
   Kind kind_;
   VariableLocation location_;
   int index_;
   int initializer_position_;
 
   // If this field is set, this variable references the stored locally bound
   // variable, but it might be shadowed by variable bindings introduced by
   // sloppy 'eval' calls between the reference scope (inclusive) and the
   // binding scope (exclusive).
   Variable* local_if_not_shadowed_;
 
   // Usage info.
   bool force_context_allocation_;  // set by variable resolver
   bool is_used_;
   InitializationFlag initialization_flag_;
   MaybeAssignedFlag maybe_assigned_;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_VARIABLES_H_