Implement proper scoping for "this" in arrow functions

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 9b86d0b51292f6291b734962af0f8912e8218f4d..fbc89d54c3ccc45f53484330bedf93e6564bab81 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -1599,7 +1599,7 @@ class VariableProxy FINAL : public Expression {
   DECLARE_NODE_TYPE(VariableProxy)
 
   bool IsValidReferenceExpression() const OVERRIDE {
-    return !is_resolved() || var()->IsValidReference();
+    return !is_this() && !is_new_target();
   }
 
   bool IsArguments() const { return is_resolved() && var()->is_arguments(); }
@@ -1621,6 +1621,8 @@ class VariableProxy FINAL : public Expression {
 
   bool is_this() const { return IsThisField::decode(bit_field_); }
 
+  bool is_new_target() const { return IsNewTargetField::decode(bit_field_); }
+
   bool is_assigned() const { return IsAssignedField::decode(bit_field_); }
   void set_is_assigned() {
     bit_field_ = IsAssignedField::update(bit_field_, true);
@@ -1655,12 +1657,13 @@ class VariableProxy FINAL : public Expression {
  protected:
   VariableProxy(Zone* zone, Variable* var, int position);
 
-  VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
-                int position);
+  VariableProxy(Zone* zone, const AstRawString* name,
+                Variable::Kind variable_kind, int position);
 
   class IsThisField : public BitField8<bool, 0, 1> {};
   class IsAssignedField : public BitField8<bool, 1, 1> {};
   class IsResolvedField : public BitField8<bool, 2, 1> {};
+  class IsNewTargetField : public BitField8<bool, 3, 1> {};
 
   // Start with 16-bit (or smaller) field, which should get packed together
   // with Expression's trailing 16-bit field.
@@ -3358,9 +3361,9 @@ class AstNodeFactory FINAL BASE_EMBEDDED {
   }
 
   VariableProxy* NewVariableProxy(const AstRawString* name,
-                                  bool is_this,
+                                  Variable::Kind variable_kind,
                                   int position = RelocInfo::kNoPosition) {
-    return new (zone_) VariableProxy(zone_, name, is_this, position);
+    return new (zone_) VariableProxy(zone_, name, variable_kind, position);
   }
 
   Property* NewProperty(Expression* obj, Expression* key, int pos) {