Add cleanup for measurements that use tracing

tools/perf/measurements/smoothness_controller.py

Index: tools/perf/measurements/smoothness_controller.py
diff --git a/tools/perf/measurements/smoothness_controller.py b/tools/perf/measurements/smoothness_controller.py
index d8b804d238eb17d4789a735a3954a80898870343..ad64a597b81bc19893abdbe2b36e2494261ec658 100644
--- a/tools/perf/measurements/smoothness_controller.py
+++ b/tools/perf/measurements/smoothness_controller.py
@@ -63,3 +63,7 @@ class SmoothnessController(object):
         if r.value is None:
           raise MissingDisplayFrameRateError(r.name)
         results.Add(r.name, r.unit, r.value)
+
+  def CleanUp(self, tab):

[ernstm, 2014/03/25 00:00:53]

Can you please add:
if tab.browser.platform.IsRawDisplayFrameRateSupported():
  tab.browser.platform.StopRawDisplayFrameRateMeasurement()

That would probably fix crbug.com/355773 (assuming this is meant to be called
from an exception handler and such handler is already in place).

+    if tab.browser.is_tracing_running:
+      tab.browser.StopTracing()