Fix MarkKeyParser crash when changing keyconfig.

Ensure MarkKeyParser implements on_keyconfig_changed, so it doesn't fail when
rebinding a key. It doesn't have keybindings, so the implementation is just
`pass`.

This also fixes a few flake8 style errors.

qutebrowser/keyinput/modeparsers.py

@@ -254,7 +254,6 @@ class MarkKeyParser(keyparser.BaseKeyParser):
         Return:
             True if event has been handled, False otherwise.
         """
-
         if utils.keyevent_to_string(e) is None:
             # this is a modifier key, let it pass and keep going
             return True
@@ -279,3 +278,11 @@ class MarkKeyParser(keyparser.BaseKeyParser):
         self.request_leave.emit(self._mode, "valid mark key")
 
         return True
+
+    def on_keyconfig_changed(self, mode):
+        """MarkKeyParser has no config section (no bindable keys)."""
+        pass
+
+    def execute(self, cmdstr, _keytype, count=None):
+        """Should never be called on MarkKeyParser."""
+        raise NotImplementedError

qutebrowser/mainwindow/tabbedbrowser.py

@@ -23,15 +23,15 @@ import functools
 import collections
 
 from PyQt5.QtWidgets import QSizePolicy
-from PyQt5.QtCore import pyqtSignal, pyqtSlot, QTimer, QUrl, QPoint
+from PyQt5.QtCore import pyqtSignal, pyqtSlot, QTimer, QUrl
 from PyQt5.QtGui import QIcon
 
 from qutebrowser.config import config
 from qutebrowser.keyinput import modeman
 from qutebrowser.mainwindow import tabwidget
 from qutebrowser.browser import signalfilter, webview
-from qutebrowser.utils import (log, usertypes, utils, qtutils, objreg, urlutils,
+from qutebrowser.utils import (log, usertypes, utils, qtutils, objreg,
-                               message)
+                               urlutils, message)
 
 
 UndoEntry = collections.namedtuple('UndoEntry', ['url', 'history'])

tests/unit/keyinput/test_modeman.py

@@ -22,14 +22,17 @@ import pytest
 from qutebrowser.keyinput import modeman as modeman_module
 from qutebrowser.utils import usertypes
 
-from PyQt5.QtCore import Qt
+from PyQt5.QtCore import Qt, QObject, pyqtSignal
 
 
-class FakeKeyparser:
+class FakeKeyparser(QObject):
 
     """A fake BaseKeyParser which doesn't handle anything."""
 
+    request_leave = pyqtSignal(usertypes.KeyMode, str)
+
     def __init__(self):
+        super().__init__()
         self.passthrough = False
 
     def handle(self, evt):