[strong] Make strong 'this' optional for experimentation

src/parser.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/bailout-reason.h"
 #include "src/base/platform/platform.h"
@@ skipping 2545 matching lines @@
     case Token::FUNCTION:
     case Token::LBRACE:
       UNREACHABLE();  // Always handled by the callers.
     case Token::CLASS:
       ReportUnexpectedToken(Next());
       *ok = false;
       return nullptr;
 
     case Token::THIS:
     case Token::SUPER:
-      if (is_strong(language_mode()) &&
+      if ((FLAG_strong_this || peek() != Token::THIS) &&

[conradw, 2015/06/12 15:01:34]

Could the peek() check be eliminated by shifting the flag check to if
(!FLAG_strong_this) { break; } in the THIS case with a fallthrough?

[rossberg, 2015/06/15 08:50:30]

Done.

+          is_strong(language_mode()) &&
           i::IsConstructor(function_state_->kind())) {
         bool is_this = peek() == Token::THIS;
         Expression* expr;
         ExpressionClassifier classifier;
         if (is_this) {
           expr = ParseStrongInitializationExpression(&classifier, CHECK_OK);
         } else {
           expr = ParseStrongSuperCallExpression(&classifier, CHECK_OK);
         }
         ValidateExpression(&classifier, CHECK_OK);
@@ skipping 3247 matching lines @@
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(
       ast_value_factory()->reflect_construct_string(), NULL, args, pos);
 }
 }  // namespace internal
 }  // namespace v8