harmony-scoping: Allow 'const' iteration variables in strict mode.

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index fd82651a7e012a88c7e09c58c53732522853d121..a53abfe4ff3af732cd2cd46ac79db8c35264f698 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -344,14 +344,18 @@ class ParserBase : public Traits {
   }
 
   bool CheckContextualKeyword(Vector<const char> keyword) {
-    if (peek() == Token::IDENTIFIER &&
-        scanner()->is_next_contextual_keyword(keyword)) {
+    if (PeekContextualKeyword(keyword)) {
       Consume(Token::IDENTIFIER);
       return true;
     }
     return false;
   }
 
+  bool PeekContextualKeyword(Vector<const char> keyword) {
+    return peek() == Token::IDENTIFIER &&
+           scanner()->is_next_contextual_keyword(keyword);
+  }
+
   void ExpectContextualKeyword(Vector<const char> keyword, bool* ok) {
     Expect(Token::IDENTIFIER, ok);
     if (!*ok) return;