Pinned tabs are saved alongside normal tabs in a session file.
If user don't have session restore enabled, pinned tabs are saved
and restored from a special pinnedtabs.dat file which uses different
codepath.
It has also another problem that it only saves pinned tabs for last
browser window, which sometimes may be confusing and lead to losing
the pinned tabs.
Fixes issue with current tab not being loaded on session restore
with "don't load tabs until selected" option.
It was needed to switch to other tab and then switch back to first tab
to actually load it.
Also pause updates of the whole browser window when restoring session.