Telemetry: adds CPU frequency stats.

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
@@ skipping 13 matching lines @@
 
     # 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))
 
+    # The result for global frequency stats is used.
+    start = {
+      'Browser': {'CpuProcessTime': 0, 'TotalTime': 0},
+      'Global': {'GlobalCpuFrequencyStats': {'1_hz': 9, '2_hz': 19}}
+    }
+    end = {
+      'Browser': {'CpuProcessTime': 5, 'TotalTime': 20},
+      'Global': {'GlobalCpuFrequencyStats': {'1_hz': 20, '2_hz': 31}}
+    }
+
+    expected = {
+      'Browser': 0.25,
+      'Global': {'GlobalCpuFrequencyStats': {'1_hz': 11, '2_hz': 12}}
+    }
+    self.assertEqual(expected, cpu._SubtractCpuStats(end, start))