Implement proper scoping for "this" in arrow functions

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 4280a983649608aae812c1b9d260f83ca4581d49..16927e537d50d0efa2ad109dbbad95ebd3cd0943 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -71,10 +71,14 @@ VariableProxy::VariableProxy(Zone* zone, Variable* var, int position)
 }
 
 
-VariableProxy::VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
-                             Interface* interface, int position)
+VariableProxy::VariableProxy(Zone* zone,
+                             const AstRawString* name,
+                             Variable::Kind variable_kind,
+                             Interface* interface,
+                             int position)
     : Expression(zone, position),
-      bit_field_(IsThisField::encode(is_this) | IsAssignedField::encode(false) |
+      bit_field_(IsThisField::encode(variable_kind == Variable::THIS) |
+                 IsAssignedField::encode(false) |
                  IsResolvedField::encode(false)),
       variable_feedback_slot_(FeedbackVectorICSlot::Invalid()),
       raw_name_(name),