chrome копирует поведение ie
пишите так
<form>
<input type="text" id="text_form" name="text_form" value="" />
<input type="text" id="text_in" name="text_in" value="" />
<input type="button" onclick="insert_text(*!*document.getElementById('*/!*text_in*!*')*/!*.value)" value="Ввести текст" />
</form>
<script>
function insert_text(insert_var)
{
*!*document.getElementById('text_form')*/!*.value=insert_var;
}
</script>