[WIP] add statusline widget for back/forward indicator

Fixes #2737.

qutebrowser/mainwindow/statusbar/bar.py

@@ -25,8 +25,9 @@
 from qutebrowser.browser import browsertab
 from qutebrowser.config import config, style
 from qutebrowser.utils import usertypes, log, objreg, utils
-from qutebrowser.mainwindow.statusbar import (command, progress, keystring,
-                                              percentage, url, tabindex)
+from qutebrowser.mainwindow.statusbar import (backforward, command, progress,
+                                              keystring, percentage, url,
+                                              tabindex)
 from qutebrowser.mainwindow.statusbar import text as textwidget
 
 
@@ -184,6 +185,9 @@ def __init__(self, *, win_id, private, parent=None):
         self.percentage = percentage.Percentage()
         self._hbox.addWidget(self.percentage)
 
+        self.backforward = backforward.Backforward()
+        self._hbox.addWidget(self.backforward)
+
         self.tabindex = tabindex.TabIndex()
         self._hbox.addWidget(self.tabindex)
 
@@ -321,6 +325,7 @@ def on_tab_changed(self, tab):
         self.url.on_tab_changed(tab)
         self.prog.on_tab_changed(tab)
         self.percentage.on_tab_changed(tab)
+        self.backforward.on_tab_changed(tab)
         self.maybe_hide()
         assert tab.private == self._color_flags.private