[es6] emit error when for-in loop declarations are initialized in strict mode

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index 08963c942540f05f97a1893a5166b243522a56d7..8603ab69b32e29fc1a0ddd282f0387c0b422c1d1 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -1596,6 +1596,7 @@ class PreParser : public ParserBase<PreParserTraits> {
   Statement ParseVariableDeclarations(VariableDeclarationContext var_context,
                                       VariableDeclarationProperties* decl_props,
                                       int* num_decl,
+                                      Scanner::Location* first_initializer_loc,
                                       bool* ok);
   Statement ParseExpressionOrLabelledStatement(bool* ok);
   Statement ParseIfStatement(bool* ok);