Telemetry: adds CPU frequency stats.

tools/perf/metrics/cpu_unittest.py

Index: tools/perf/metrics/cpu_unittest.py
diff --git a/tools/perf/metrics/cpu_unittest.py b/tools/perf/metrics/cpu_unittest.py
index 30d488dac8bc420399e00f32ea8a6fff6b8277d0..0b5b14b5d194fa7037c12b7d8399b3ef0d4391aa 100644
--- a/tools/perf/metrics/cpu_unittest.py
+++ b/tools/perf/metrics/cpu_unittest.py
@@ -31,3 +31,18 @@ class CpuMetricTest(unittest.TestCase):
     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))