[Telemetry] Update expectations for testPowerMonitoringSync.

We no longer sample output and energy_consumption_mwh is the canonical final
metric. This didn't show up on the unittesting bots because they don't run
10.9 where we can measure power.

BUG=400606

Review URL: https://codereview.chromium.org/446593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287594 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/platform/platform_backend_unittest.py

@@ -28,5 +28,5 @@ class PlatformBackendTest(unittest.TestCase):
     backend.StartMonitoringPower(browser_mock)
     time.sleep(0.001)
     output = backend.StopMonitoringPower()
-    self.assertTrue(output.has_key('power_samples_mw'))
+    self.assertTrue(output.has_key('energy_consumption_mwh'))
     self.assertTrue(output.has_key('identifier'))