Don't rely only on __del__ to cleanup PowerMetric when Smoothness.DidRunActions is not called.

tools/perf/measurements/smoothness_unittest.py

Index: tools/perf/measurements/smoothness_unittest.py
diff --git a/tools/perf/measurements/smoothness_unittest.py b/tools/perf/measurements/smoothness_unittest.py
index e537399237661481f02e767b04604c9ba982a614..e210dc4ef029b2584f973b6f0bc821fe0a446ba2 100644
--- a/tools/perf/measurements/smoothness_unittest.py
+++ b/tools/perf/measurements/smoothness_unittest.py
@@ -4,9 +4,11 @@
 import sys
 
 from measurements import smoothness
+from telemetry.core import exceptions
 from telemetry.core import wpr_modes
 from telemetry.page import page
 from telemetry.page import page_measurement_unittest_base
+from telemetry.page import page_test
 from telemetry.unittest import options_for_unittests
 
 class FakePlatform(object):
@@ -131,3 +133,37 @@ class SmoothnessUnitTest(
 
   def testCleanUpTrace(self):
     self.TestTracingCleanedUp(smoothness.Smoothness, self._options)
+
+  def testCleanUpPowerMetric(self):
+    class FailPage(page.Page):
+      def __init__(self, page_set):
+        super(FailPage, self).__init__(
+            url='file://blank.html',
+            page_set=page_set, base_dir=page_set.base_dir)
+      def RunSmoothness(self, _):
+        raise exceptions.IntentionalException
+
+    ps = self.CreateEmptyPageSet()
+    ps.AddPage(FailPage(ps))
+
+    start_measuring_called = [False]
+    stop_measuring_called = [False]
+    class BuggyMeasurement(smoothness.Smoothness):
+      # Inject fake measuring_power methods to browser
+      def WillStartBrowser(self, browser):
+        super(BuggyMeasurement, self).WillStartBrowser(browser)
+        def FakeStart(_1, _2):
+          start_measuring_called[0] = True
+        def FakeStop(_1, _2):
+          stop_measuring_called[0] = True
+        self._power_metric.Start = FakeStart
+        self._power_metric.Stop = FakeStop
+
+    measurement = BuggyMeasurement()
+    try:
+      self.RunMeasurement(measurement, ps)
+    except page_test.TestNotSupportedOnPlatformFailure:
+      pass
+
+    self.assertTrue(start_measuring_called[0])
+    self.assertTrue(stop_measuring_called[0])