Regress the metric reported by dummy_benchmark.stable_benchmark_1 by 20%

*PERF SHERRIF: this CL intentionally regressions dummy_benchmark.stable_benchmark_1 for bisect FYI.
We are doing this to refresh the revision ranges used by bisect FYI jobs.

BUG=646628
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.perf:linux_perf_cq;master.tryserver.chromium.perf:mac_retina_perf_cq;master.tryserver.chromium.perf:winx64_10_perf_cq

Review-Url: https://codereview.chromium.org/2337323002
Cr-Commit-Position: refs/heads/master@{#418687}

tools/perf/benchmarks/dummy_benchmark.py

@@ -43,7 +43,7 @@ class DummyBenchmarkOne(_DummyBenchmark):
   """A low noise benchmark with mean=100 & std=1."""
 
   def CreatePageTest(self, options):
-    return _DummyTest(140, 1)
+    return _DummyTest(168, 1)
 
   @classmethod
   def Name(cls):