Add change event handler which toggles placeholder visibility if value changes to or from empty.
Add change event handler which toggles placeholder visibility if value changes to or from empty.

This will make the placeholders behave well with programmatic input field value changes as long as the change event is fired along with a value change.

The motivation for this change came from password manager browser extensions which pre-fill form fields.

ginader/HTML5-placeholder-polyfill,ginader/HTML5-placeholder-polyfill,ginader/HTML5-placeholder-polyfill