cmdline client: Improve error message when passing an empty TraceConfig am: 21bf7f8144 am: 1056538eab am: 681fca136c
cmdline client: Improve error message when passing an empty TraceConfig am: 21bf7f8144 am: 1056538eab
am: 681fca136c

Change-Id: I433bb61a0dedbda7d39e7b4e43efda99cf85efef

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto