Polymer clears the value of window.performance

[attilapuskas]

In the Polymer class the performance field has been introduced: here which makes the previously not null performance undefined. This causes an exception for example in iron-list.html where the window.performance.now() is called without checking whether the performance has a value or not.

[frami]

We have the same problem. We always have to comment out this part of the Polymer class.

[cpboyd]

When compiling, I get a possibly related warning:

[INFO] [WARN] Exporting effectively non-final field com.vaadin.polymer.Polymer.performance. Due to the way exporting works, the value of the exported field will not be reflected across Java/JavaScript border.

[manolo]

Seems introduced by mistake