perf top: Allow disabling/enabling events dynamicly

Now it is possible to press CTRL+z at anytime and that will disable the
events being monitored, essentially turning 'top' into 'report', with
pressing CTRL+z again making it enable the events again, returning to
the 'top' behaviour, i.e. dynamic + decaying of older samples.

One may want, for instance, play with:

    -d, --delay <n>       number of seconds to delay between refreshes

and:

    -z, --zero            zero history across updates

Plus CTRL+z to see only the events since last zeroing, etc.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-zq7tnh5462blt2yda0bcxh5b@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/browsers/hists.c

@@ -1736,6 +1736,7 @@ static int perf_evsel__hists_browse(struct perf_evsel *evsel, int nr_events,
 	"t             Zoom into current Thread\n"
 	"V             Verbose (DSO names in callchains, etc)\n"
 	"z             Toggle zeroing of samples\n"
+	"CTRL+z        Enable/Disable events\n"
 	"/             Filter symbol by name";
 
 	if (browser == NULL)
@@ -1900,6 +1901,7 @@ static int perf_evsel__hists_browse(struct perf_evsel *evsel, int nr_events,
 			/* Fall thru */
 		case 'q':
 		case CTRL('c'):
+		case CTRL('z'):
 			goto out_free_stack;
 		default:
 			continue;