Global link hints; focus window for selectable elements.
Global link hints; focus window for selectable elements.

Because we're running hint modes in multiple frames, we need to ensure
the right frame has the focus for selectable elements (inputs).

willsALMANJ/vimium,decaffeinate-examples/vimium,mrmr1993/vimium,poacher2k/vimium,gdh1995/vimium,smblott-github/vimium,poacher2k/vimium,willsALMANJ/vimium,decaffeinate-examples/vimium,willsALMANJ/vimium,poacher2k/vimium,mrmr1993/vimium,mrmr1993/vimium,philc/vimium,philc/vimium,smblott-github/vimium,smblott-github/vimium,gdh1995/vimium,philc/vimium,decaffeinate-examples/vimium,gdh1995/vimium