[strong] Deprecate delete

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 2479 matching lines @@
   //   '-' UnaryExpression
   //   '~' UnaryExpression
   //   '!' UnaryExpression
 
   Token::Value op = peek();
   if (Token::IsUnaryOp(op)) {
     op = Next();
     int pos = position();
     ExpressionT expression = ParseUnaryExpression(CHECK_OK);
 
-    // "delete identifier" is a syntax error in strict mode.
-    if (op == Token::DELETE && is_strict(language_mode()) &&
-        this->IsIdentifier(expression)) {
-      ReportMessage("strict_delete");
-      *ok = false;
-      return this->EmptyExpression();
+    if (op == Token::DELETE && is_strict(language_mode())) {
+      if (is_strong(language_mode())) {
+        ReportMessage("strong_delete");
+        *ok = false;
+        return this->EmptyExpression();
+      } else if (this->IsIdentifier(expression)) {
+        // "delete identifier" is a syntax error in strict mode.
+        ReportMessage("strict_delete");
+        *ok = false;
+        return this->EmptyExpression();
+      }
     }
 
     // Allow Traits do rewrite the expression.
     return this->BuildUnaryExpression(expression, op, pos, factory());
   } else if (Token::IsCountOp(op)) {
     op = Next();
     Scanner::Location lhs_location = scanner()->peek_location();
     ExpressionT expression = this->ParseUnaryExpression(CHECK_OK);
     expression = this->CheckAndRewriteReferenceExpression(
         expression, lhs_location, "invalid_lhs_in_prefix_op", CHECK_OK);
@@ skipping 560 matching lines @@
       *ok = false;
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H