Add cleanup for measurements that use tracing

BUG=348271

1st commit: https://src.chromium.org/viewvc/chrome?view=rev&revision=259808

NOTRY=True

Review URL: https://codereview.chromium.org/208643007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260454 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/measurements/smoothness_controller.py

@@ -65,5 +65,7 @@ class SmoothnessController(object):
         results.Add(r.name, r.unit, r.value)
 
   def CleanUp(self, tab):
+    if tab.browser.platform.IsRawDisplayFrameRateSupported():
+      tab.browser.platform.StopRawDisplayFrameRateMeasurement()
     if tab.browser.is_tracing_running:
       tab.browser.StopTracing()