[Telemetry] Improve _GetProcJiffies operation with using grep.

tools/telemetry/telemetry/core/platform/linux_based_platform_backend_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 logging
 import os
 import unittest
 
 from telemetry.core.platform import linux_based_platform_backend
 from telemetry.core import util
 
+util.AddDirToPythonPath(util.GetTelemetryDir(), 'third_party', 'mock')
+import mock  # pylint: disable=import-error
+
+
 
 class TestBackend(linux_based_platform_backend.LinuxBasedPlatformBackend):
 
   # pylint: disable=W0223
 
   def __init__(self):
     super(TestBackend, self).__init__()
     self._mock_files = {}
 
   def SetMockFile(self, filename, output):
@@ skipping 19 matching lines @@
 
     backend = TestBackend()
     self.SetMockFileInBackend(backend, 'stat', '/proc/1/stat')
     result = backend.GetCpuStats(1)
     self.assertEquals(result, {'CpuProcessTime': 22.0})
 
   def testGetCpuTimestampBasic(self):
     if not linux_based_platform_backend.resource:
       logging.warning('Test not supported')
       return
-
-    backend = TestBackend()
-    self.SetMockFileInBackend(backend, 'timer_list', '/proc/timer_list')
-    result = backend.GetCpuTimestamp()
-    self.assertEquals(result, {'TotalTime': 105054633.0})
+    jiffies_grep_string = """
+    jiffies
+jiffies  a1111
+    jiffies: 10505463300

[aiolos (Not reviewing), 2015/04/25 03:03:16]

nit: Could you add a line for '.last_jiffies' like it had in the origional file
as well?

[nednguyen, 2015/04/25 04:10:23]

Done.

+    jiffies: 10505463333
+    """
+    with mock.patch.object(
+        linux_based_platform_backend.LinuxBasedPlatformBackend,
+        'RunCommand', return_value=jiffies_grep_string) as mock_method:
+      backend = linux_based_platform_backend.LinuxBasedPlatformBackend()
+      result = backend.GetCpuTimestamp()
+      self.assertEquals(result, {'TotalTime': 105054633.0})
+    mock_method.assert_call_once_with(
+        ['grep', '-m', '1', 'jiffies:','/proc/timer_list'])
 
   def testGetMemoryStatsBasic(self):
     if not linux_based_platform_backend.resource:
       logging.warning('Test not supported')
       return
 
     backend = TestBackend()
     self.SetMockFileInBackend(backend, 'stat', '/proc/1/stat')
     self.SetMockFileInBackend(backend, 'status', '/proc/1/status')
     self.SetMockFileInBackend(backend, 'smaps', '/proc/1/smaps')
@@ skipping 12 matching lines @@
     backend = TestBackend()
     self.SetMockFileInBackend(backend, 'stat', '/proc/1/stat')
     self.SetMockFileInBackend(backend, 'status_nohwm', '/proc/1/status')
     self.SetMockFileInBackend(backend, 'smaps', '/proc/1/smaps')
     result = backend.GetMemoryStats(1)
     self.assertEquals(result, {'PrivateDirty': 5324800,
                                'VM': 1025978368,
                                'VMPeak': 1025978368,
                                'WorkingSetSize': 84000768,
                                'WorkingSetSizePeak': 84000768})