perfetto: Add a testing program

It's often hard to know if we're dropping data from ftrace, the systrace
UI is naturally gappy when the CPUs are idle. Skippy is a test program
that produces visually identifiable output in the systrace UI for
debugging dropped data. Skippy is so named because it skips between
CPU cores to produce the pattern.

Change-Id: I3409b5271f2562c857d19b9fc55a517d9161212d
diff --git a/BUILD.gn b/BUILD.gn
index 6f8b7b2..74e972e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -47,6 +47,7 @@
         ":perfetto_integrationtests",
         ":traced",
         ":traced_probes",
+        "tools/skippy",
       ]
     }
   }