WebEngine: Fake keypresses with modifiers instead of override_target

With QtWebEngine, handling a click (e.g. createWindow being called)
happens some time after a click event has been handled.

When setting override_target, that means we don't know when to set the
override target back, and we can't simply only unset it in createWindow
as elements not causing a new tab to be opened (like an input field) can
be hinted too.

Instead, we now only use override_target with QtWebKit, and simply
generate fake key events with the right modifiers to do the right thing
in createWindow for QtWebEngine.

Fixes #2119.

qutebrowser/browser/browsertab.py

@@ -84,6 +84,7 @@ class TabData:
         inspector: The QWebInspector used for this webview.
         viewing_source: Set if we're currently showing a source view.
         override_target: Override for open_target for fake clicks (like hints).
+                         Only used for QtWebKit.
     """
 
     def __init__(self):

qutebrowser/browser/webelem.py

@@ -338,6 +338,8 @@ class AbstractWebElement(collections.abc.MutableMapping):
         """Simulate a click on the element."""
         # FIXME:qtwebengine do we need this?
         # self._widget.setFocus()
+
+        # For QtWebKit
         self._tab.data.override_target = click_target
 
         pos = self._mouse_pos()
@@ -345,20 +347,24 @@ class AbstractWebElement(collections.abc.MutableMapping):
         log.webelem.debug("Sending fake click to {!r} at position {} with "
                           "target {}".format(self, pos, click_target))
 
-        if click_target in [usertypes.ClickTarget.tab,
-                            usertypes.ClickTarget.tab_bg,
-                            usertypes.ClickTarget.window]:
-            modifiers = Qt.ControlModifier
+        modifiers = {
+            usertypes.ClickTarget.normal: Qt.NoModifier,
+            usertypes.ClickTarget.window: Qt.AltModifier | Qt.ShiftModifier,
+            usertypes.ClickTarget.tab: Qt.ControlModifier,
+            usertypes.ClickTarget.tab_bg: Qt.ControlModifier,
+        }
+        if config.get('tabs', 'background-tabs'):
+            modifiers[usertypes.ClickTarget.tab] |= Qt.ShiftModifier
         else:
-            modifiers = Qt.NoModifier
+            modifiers[usertypes.ClickTarget.tab_bg] |= Qt.ShiftModifier
 
         events = [
             QMouseEvent(QEvent.MouseMove, pos, Qt.NoButton, Qt.NoButton,
                         Qt.NoModifier),
             QMouseEvent(QEvent.MouseButtonPress, pos, Qt.LeftButton,
-                        Qt.LeftButton, modifiers),
+                        Qt.LeftButton, modifiers[click_target]),
             QMouseEvent(QEvent.MouseButtonRelease, pos, Qt.LeftButton,
-                        Qt.NoButton, modifiers),
+                        Qt.NoButton, modifiers[click_target]),
         ]
 
         for evt in events:

qutebrowser/browser/webengine/webview.py

@@ -74,18 +74,12 @@ class WebEngineView(QWebEngineView):
         """
         debug_type = debug.qenum_key(QWebEnginePage, wintype)
         background_tabs = config.get('tabs', 'background-tabs')
-        override_target = self._tabdata.override_target
 
         log.webview.debug("createWindow with type {}, background_tabs "
-                          "{}, override_target {}".format(
-                              debug_type, background_tabs, override_target))
+                          "{}".format(debug_type, background_tabs))
 
-        if override_target is not None:
-            target = override_target
-            self._tabdata.override_target = None
-        elif wintype == QWebEnginePage.WebBrowserWindow:
-            log.webview.debug("createWindow with WebBrowserWindow - when does "
-                              "this happen?!")
+        if wintype == QWebEnginePage.WebBrowserWindow:
+            # Shift-Alt-Click
             target = usertypes.ClickTarget.window
         elif wintype == QWebEnginePage.WebDialog:
             log.webview.warning("{} requested, but we don't support "