Notify canGoBack/canGoForward on urlChanged instead of loadingChanged.

In order to support Fragment (#) based routing and history navigation
together, canGoBack/canGoForward properties should be notified when the
url is changed instead of when the page is loading.

Task-number: QTBUG-41849
Change-Id: Ic995fffa5c683dade88fbd98ffea90527a77261b
Reviewed-by: Michael Bruning <michael.bruning@digia.com>
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Reviewed-by: Jarred Nicholls <jarred.nicholls@gmail.com>

src/webengine/api/qquickwebengineview_p.h

@@ -54,8 +54,8 @@ class Q_WEBENGINE_PRIVATE_EXPORT QQuickWebEngineView : public QQuickItem {
     Q_PROPERTY(bool loading READ isLoading NOTIFY loadingChanged)
     Q_PROPERTY(int loadProgress READ loadProgress NOTIFY loadProgressChanged)
     Q_PROPERTY(QString title READ title NOTIFY titleChanged)
-    Q_PROPERTY(bool canGoBack READ canGoBack NOTIFY loadingChanged)
-    Q_PROPERTY(bool canGoForward READ canGoForward NOTIFY loadingChanged)
+    Q_PROPERTY(bool canGoBack READ canGoBack NOTIFY urlChanged)
+    Q_PROPERTY(bool canGoForward READ canGoForward NOTIFY urlChanged)
     Q_ENUMS(NavigationRequestAction);
     Q_ENUMS(NavigationType);
     Q_ENUMS(LoadStatus);