[es6] Introduce spec compliant IsConstructor.

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index a5aa3709a6d509174fe9c02530b80cd940c907ab..e9e0f4bfb8b620ef0872c356d07ce0ffa4edb432 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -2228,7 +2228,7 @@ ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
       if (FLAG_strong_this && is_strong(language_mode())) {
         // Constructors' usages of 'this' in strong mode are parsed separately.
         // TODO(rossberg): this does not work with arrow functions yet.
-        if (i::IsConstructor(function_state_->kind())) {
+        if (IsClassConstructor(function_state_->kind())) {
           ReportMessage(MessageTemplate::kStrongConstructorThis);
           *ok = false;
           break;
@@ -3612,7 +3612,7 @@ ParserBase<Traits>::ParseSuperExpression(bool is_new,
   Scope* scope = scope_->ReceiverScope();
   FunctionKind kind = scope->function_kind();
   if (IsConciseMethod(kind) || IsAccessorFunction(kind) ||
-      i::IsConstructor(kind)) {
+      IsClassConstructor(kind)) {
     if (peek() == Token::PERIOD || peek() == Token::LBRACK) {
       scope->RecordSuperPropertyUsage();
       return this->SuperPropertyReference(scope_, factory(), pos);