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..e82634241325ec4bd6e7c8c63cf203525f47e6af 100644
--- a/tools/perf/measurements/smoothness_unittest.py
+++ b/tools/perf/measurements/smoothness_unittest.py
@@ -4,9 +4,12 @@
 import sys
 
 from measurements import smoothness
+from metrics import power
+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 +134,38 @@ 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
+
+    class FakePowerMetric(power.PowerMetric):
+      start_called = False
+      stop_called = True
+      def Start(self, _1, _2):
+        self.start_called = True
+      def Stop(self, _1, _2):
+        self.stop_called = True
+
+    ps = self.CreateEmptyPageSet()
+    ps.AddPage(FailPage(ps))
+
+    class BuggyMeasurement(smoothness.Smoothness):
+      fake_power = None
+      # Inject fake power metric.
+      def WillStartBrowser(self, browser):
+        self.fake_power = self._power_metric = FakePowerMetric(browser)
+
+    measurement = BuggyMeasurement()
+    try:
+      self.RunMeasurement(measurement, ps)
+    except page_test.TestNotSupportedOnPlatformFailure:
+      pass
+
+    self.assertTrue(measurement.fake_power.start_called)
+    self.assertTrue(measurement.fake_power.stop_called)