[es6] Make assignment to new.target an early ReferenceError

src/preparser.cc

 // 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.
 
 #include <cmath>
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
 #include "src/conversions-inl.h"
 #include "src/conversions.h"
@@ skipping 900 matching lines @@
         Expect(Token::RPAREN, CHECK_OK);
         ParseSubStatement(CHECK_OK);
         return Statement::Default();
       }
     } else {
       Expression lhs = ParseExpression(false, CHECK_OK);
       is_let_identifier_expression =
           lhs.IsIdentifier() && lhs.AsIdentifier().IsLet();
       if (CheckInOrOf(lhs.IsIdentifier(), &mode, ok)) {
         if (!*ok) return Statement::Default();
+        // TODO(adamk): Should call CheckAndRewriteReferenceExpression here
+        // to catch early errors if lhs is not a valid reference expression.
         ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
         ParseSubStatement(CHECK_OK);
         return Statement::Default();
       }
     }
   }
 
   // Parsed initializer at this point.
   // Detect attempts at 'let' declarations in sloppy mode.
@@ skipping 268 matching lines @@
 
   DCHECK(!spread_pos.IsValid());
 
   return Expression::Default();
 }
 
 #undef CHECK_OK
 
 
 } }  // v8::internal