perf ui: Reimplement ui__popup_menu using ui__browser

Right now let it work just like the other browsers: in full screen, at
the top left corner. If people complain we can revisit, I found it OK
and the laziest/quickest approach at reusing the ui_browser ;-)

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-4bgeqizcxh04q0sk24cw43gk@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>