Revert of Improve readability of power monitoring code and add additional

tools/telemetry/telemetry/internal/platform/power_monitor/msr_power_monitor.py

Index: tools/telemetry/telemetry/internal/platform/power_monitor/msr_power_monitor.py
diff --git a/tools/telemetry/telemetry/internal/platform/power_monitor/msr_power_monitor.py b/tools/telemetry/telemetry/internal/platform/power_monitor/msr_power_monitor.py
index 5cf3d16e5d3aa97e7041a97dd093b521876c86a7..4214adddf4327f1b5c03588ad3bf420909b816e4 100644
--- a/tools/telemetry/telemetry/internal/platform/power_monitor/msr_power_monitor.py
+++ b/tools/telemetry/telemetry/internal/platform/power_monitor/msr_power_monitor.py
@@ -42,12 +42,15 @@
     raise NotImplementedError()
 
   def StartMonitoringPower(self, browser):
-    self._CheckStart()
+    assert self._start_energy_j is None and self._start_temp_c is None, (
+        'Called StartMonitoringPower() twice.')
     self._start_energy_j = self._PackageEnergyJoules()
     self._start_temp_c = self._TemperatureCelsius()
 
   def StopMonitoringPower(self):
-    self._CheckStop()
+    assert not(self._start_energy_j is None or self._start_temp_c is None), (
+        'Called StopMonitoringPower() before StartMonitoringPower().')
+
     energy_consumption_j = self._PackageEnergyJoules() - self._start_energy_j
     average_temp_c = (self._TemperatureCelsius() + self._start_temp_c) / 2.
     if energy_consumption_j < 0:  # Correct overflow.