Implement proper scoping for "this" in arrow functions

src/variables.h

Index: src/variables.h
diff --git a/src/variables.h b/src/variables.h
index 93bfb4a1816aeb3fb9f370c847ace86da6f2d6b3..1a0ad6a99da70082c67ee1d27fb4bdfb18ad4966 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -53,15 +53,13 @@ class Variable: public ZoneObject {
   };
 
   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
@@ -150,9 +148,6 @@ class Variable: public ZoneObject {
   // 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_;