Add reinit method for preserve-on-refresh UIs (#12191)

UI.reinit() is now called when an existing, preserved UI is shown after a
browser reload of the current page. The default implementation is empty.
The browser window size and location are up to date in UI.reinit();
window resize and URI fragment listeners, if any, will be called after
returning from UI.reinit().

Change-Id: Ie7aa670aaecf8e0e1510c91325b2a137b41263af