Implement proper scoping for "this" in arrow functions

src/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_VARIABLES_H_
 #define V8_VARIABLES_H_
 
 #include "src/ast-value-factory.h"
 #include "src/interface.h"
 #include "src/zone.h"
@@ skipping 35 matching lines @@
     // corresponding scope.
     CONTEXT,
 
     // A named slot in a heap context.  name() is the variable name in the
     // context object on the heap, with lookup starting at the current
     // context.  index() is invalid.
     LOOKUP
   };
 
   Variable(Scope* scope, const AstRawString* name, VariableMode mode,
-           bool is_valid_ref, Kind kind, InitializationFlag initialization_flag,
+           Kind kind, InitializationFlag initialization_flag,
            MaybeAssignedFlag maybe_assigned_flag = kNotAssigned,
            Interface* interface = Interface::NewValue());
 
   // Printing support
   static const char* Mode2String(VariableMode mode);
 
-  bool IsValidReference() { return is_valid_ref_; }
-
   // The source code for an eval() call may refer to a variable that is
   // in an outer scope about which we don't know anything (it may not
   // be the script scope). scope() is NULL in that case. Currently the
   // scope is only used to follow the context chain length.
   Scope* scope() const { return scope_; }
 
   Handle<String> name() const { return name_->string(); }
   const AstRawString* raw_name() const { return name_; }
   VariableMode mode() const { return mode_; }
   bool has_forced_context_allocation() const {
@@ skipping 68 matching lines @@
   Location 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_;
 
-  // Valid as a reference? (const and this are not valid, for example)
-  bool is_valid_ref_;
-
   // Usage info.
   bool force_context_allocation_;  // set by variable resolver
   bool is_used_;
   InitializationFlag initialization_flag_;
   MaybeAssignedFlag maybe_assigned_;
 
   // Module type info.
   Interface* interface_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_VARIABLES_H_