[Mac] Observe the activeURL property to keep the MiniBrowser URL field up to date

[Mac] Observe the activeURL property to keep the MiniBrowser URL field up to date
https://bugs.webkit.org/show_bug.cgi?id=125579

Reviewed by Anders Carlsson.

* MiniBrowser/mac/WK2BrowserWindowController.m:
(-[WK2BrowserWindowController dealloc]): Stop observing the activeURL property.
(-[WK2BrowserWindowController observeValueForKeyPath:ofObject:change:context:]): When the
activeURL property changes, update the URL field with its value.
(-[WK2BrowserWindowController awakeFromNib]): Start observing the activeURL property.
(-[WK2BrowserWindowController browsingContextControllerDidStartProvisionalLoad:]): Just log.
(-[WK2BrowserWindowController browsingContextControllerDidReceiveServerRedirectForProvisionalLoad:]):
Ditto.
(-[WK2BrowserWindowController browsingContextController:didFailProvisionalLoadWithError:]):
Ditto.
(-[WK2BrowserWindowController browsingContextControllerDidCommitLoad:]): Ditto.
(-[WK2BrowserWindowController browsingContextController:didFailLoadWithError:]): Ditto.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@160433 268f45cc-cd09-0410-ab3c-d52691b4dbfc