Strawman: check strong mode free variables against the global object.

src/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_SCOPES_H_
 #define V8_SCOPES_H_
 
 #include "src/ast.h"
 #include "src/pending-compilation-error-handler.h"
 #include "src/zone.h"
@@ skipping 397 matching lines @@
 
   // The ModuleDescriptor for this scope; only for module scopes.
   ModuleDescriptor* module() const { return module_descriptor_; }
 
   // ---------------------------------------------------------------------------
   // Variable allocation.
 
   // Collect stack and context allocated local variables in this scope. Note
   // that the function variable - if present - is not collected and should be
   // handled separately.
-  void CollectStackAndContextLocals(ZoneList<Variable*>* stack_locals,
-                                    ZoneList<Variable*>* context_locals);
+  void CollectStackAndContextLocals(
+      ZoneList<Variable*>* stack_locals, ZoneList<Variable*>* context_locals,
+      ZoneList<Variable*>* strong_mode_free_variables = nullptr);
 
   // Current number of var or const locals.
   int num_var_or_const() { return num_var_or_const_; }
 
   // Result of variable allocation.
   int num_stack_slots() const { return num_stack_slots_; }
   int num_heap_slots() const { return num_heap_slots_; }
 
   int StackLocalCount() const;
   int ContextLocalCount() const;
@@ skipping 297 matching lines @@
 
   AstValueFactory* ast_value_factory_;
   Zone* zone_;
 
   PendingCompilationErrorHandler pending_error_handler_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCOPES_H_