perf report has a --time option to limit the time range of output.  It
only supports absolute time.

Now this option is extended to support multiple time ranges and support
the percent of time.

For example:

1. Select the first and second 10% time slices:

perf report --time 10%/1,10%/2

2. Select from 0% to 10% and 30% to 40% slices:

perf report --time 0%-10%,30%-40%

Changelog:

v6: Fix the merge issue with latest perf/core branch.
    No functional changes.

v5: Add checking of first/last sample time to detect if it's recorded
    in perf.data. If it's not recorded, returns error message to user.

v4: Remove perf_time__skip_sample, only uses perf_time__ranges_skip_sample

v3: Since the definitions of first_sample_time/last_sample_time
    are moved from perf_session to perf_evlist so change the
    related code.
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1512738826-2628-6-git-send-email-yao.jin@linux.intel.com
[ Add missing colons at end of examples in the man page ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>