[Telemetry + tools/perf] Modify the pylint disable message to use symbolic name

tools/perf/metrics/cpu_unittest.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import unittest
 
 from metrics import cpu
 
 # Testing private method.
-# pylint: disable=W0212
+# pylint: disable=protected-access
 class CpuMetricTest(unittest.TestCase):
   def testSubtractCpuStats(self):
     # The result computed is a ratio of cpu time used to time elapsed.
     start = {'Browser': {'CpuProcessTime': 0, 'TotalTime': 0}}
     end = {'Browser': {'CpuProcessTime': 5, 'TotalTime': 20}}
     self.assertEqual({'Browser': 0.25}, cpu._SubtractCpuStats(end, start))
 
     # An error is thrown if the args are called in the wrong order.
     self.assertRaises(AssertionError, cpu._SubtractCpuStats, start, end)
 
     # An error is thrown if there's a process type in end that's not in start.
     end['Renderer'] = {'CpuProcessTime': 2, 'TotalTime': 20}
     self.assertRaises(AssertionError, cpu._SubtractCpuStats, end, start)
 
     # A process type will be ignored if there's an empty dict for start or end.
     start['Renderer'] = {}
     self.assertEqual({'Browser': 0.25}, cpu._SubtractCpuStats(end, start))
 
     # Results for multiple process types can be computed.
     start['Renderer'] = {'CpuProcessTime': 0, 'TotalTime': 0}
     self.assertEqual({'Browser': 0.25, 'Renderer': 0.1},
                      cpu._SubtractCpuStats(end, start))
 
     # Test 32-bit overflow.
     start = {'Browser': {'CpuProcessTime': 0, 'TotalTime': 2**32 - 20}}
     end = {'Browser': {'CpuProcessTime': 5, 'TotalTime': 20}}
     self.assertEqual({'Browser': 0.125}, cpu._SubtractCpuStats(end, start))
     self.assertRaises(AssertionError, cpu._SubtractCpuStats, start, end)