Attempting to set the window title of a BrowserDock that is closed, then
opening the BrowserDock, would show that BrowserDock with an incorrect
title. We can handle this by overriding the showEvent of BrowserDock and
manually setting the window title after the showEvent is called,
hopefully ensuring that we are only setting the window title on a window
that exists.
Works around a bug in Qt where setWindowTitle called on a native window
that hasn't been initialised yet causes the title data to be lost,
resulting in the window's title never being set.
After cleaning up the native flags in various places, and disabling
making sibling of native widgets native, BrowserDock was left in an
inconsistent state, since it requires being native for CEF to work
properly.
Make BrowserDock native.
