perf ui browser: Add filter method

Its becoming common to allow the user to filter out parts of the data
structure being browsed, like already done in the hists browser and in
the annotate browser in the next commit, so provide it directly in the
ui_browser class list_head helpers.

More work required to move the equivalent routines found now in the
hists browser to the rb_tree helpers.

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-jk7danyt1d9ji4e3o2xuthpn@git.kernel.org


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