Beautify syntax error for unterminated argument list

src/preparser.h

 // Copyright 2012 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_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/v8.h"
 
 #include "src/bailout-reason.h"
@@ skipping 2306 matching lines @@
   bool done = (peek() == Token::RPAREN);
   while (!done) {
     ExpressionT argument = this->ParseAssignmentExpression(
         true, CHECK_OK_CUSTOM(NullExpressionList));
     result->Add(argument, zone_);
     if (result->length() > Code::kMaxArguments) {
       ReportMessage("too_many_arguments");
       *ok = false;
       return this->NullExpressionList();
     }
-    done = (peek() == Token::RPAREN);
+    done = (peek() != Token::COMMA);
     if (!done) {
-      // Need {} because of the CHECK_OK_CUSTOM macro.
-      Expect(Token::COMMA, CHECK_OK_CUSTOM(NullExpressionList));
+      Next();
     }
   }
-  Expect(Token::RPAREN, CHECK_OK_CUSTOM(NullExpressionList));
+  Scanner::Location location = scanner_->location();
+  if (Token::RPAREN != Next()) {
+    ReportMessageAt(location, "unterminated_arg_list");
+    *ok = false;
+    return this->NullExpressionList();
+  }
   return result;
 }
 
 // Precedence = 2
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN, bool* ok) {
   // AssignmentExpression ::
   //   ConditionalExpression
   //   ArrowFunction
@@ skipping 805 matching lines @@
       *ok = false;
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H