[CT] Improve error message in Perf when there are no results outputted
[CT] Improve error message in Perf when there are no results outputted

BUG=skia:3920
TBR=jcgregorio

Review URL: https://codereview.chromium.org/1168303005

google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot