[telemetry] Add new measurement that counts number of GCs needed to free V8 context.

tools/perf/measurements/v8_detached_context_age_in_gc_unittest.py

Index: tools/perf/measurements/v8_detached_context_age_in_gc_unittest.py
diff --git a/tools/perf/measurements/v8_detached_context_age_in_gc_unittest.py b/tools/perf/measurements/v8_detached_context_age_in_gc_unittest.py
new file mode 100644
index 0000000000000000000000000000000000000000..ed34e016e44c473f200b5650ca00793b22581bf1
--- /dev/null
+++ b/tools/perf/measurements/v8_detached_context_age_in_gc_unittest.py
@@ -0,0 +1,98 @@
+# Copyright 2015 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.
+
+from measurements import v8_detached_context_age_in_gc
+from telemetry.core import wpr_modes
+from telemetry.page import page_test
+from telemetry.page import page as page_module
+from telemetry.results import page_test_results
+from telemetry.unittest_util import options_for_unittests
+from telemetry.unittest_util import page_test_test_case
+from telemetry.value import skip
+
+
+class FakePage(object):
+  def __init__(self, url):
+    self.url = url
+    self.is_file = url.startswith('file://')
+
+
+class FakeTab(object):
+  def __init__(self, histograms):
+    self.histograms = histograms
+    self.current_histogram_index = 0
+
+  def EvaluateJavaScript(self, script):
+    if 'V8.DetachedContextAgeInGC' in script:
+      self.current_histogram_index += 1
+      return self.histograms[self.current_histogram_index - 1]
+    return '{}'
+
+  def CollectGarbage(self):
+    pass
+
+
+def _MeasureFakePage(histograms):
+    results = page_test_results.PageTestResults()
+    page = FakePage('file://blank.html')
+    tab = FakeTab(histograms)
+    metric = v8_detached_context_age_in_gc.V8DetachedContextAgeInGC()
+    results.WillRunPage(page)
+    metric.DidNavigateToPage(page, tab)
+    metric.ValidateAndMeasurePage(page, tab, results)
+    results.DidRunPage(page)
+    return results
+
+
+def _ActualValues(results):
+  return dict((v.name, v) for v in results.all_page_specific_values)
+
+
+class SimplePage(page_module.Page):
+    def __init__(self, page_set):
+      super(SimplePage, self).__init__(
+          'file://host.html', page_set, page_set.base_dir)
+    def RunPageInteractions(self, action_runner):
+      # Reload the page to detach the previous context.
+      action_runner.ReloadPage()
+
+
+class V8DetachedContextAgeInGCTests(page_test_test_case.PageTestTestCase):
+
+  def setUp(self):
+    self._options = options_for_unittests.GetCopy()
+    self._options.browser_options.wpr_mode = wpr_modes.WPR_OFF
+
+  def testWithNoData(self):
+    histograms = [
+        """{"count": 0, "buckets": []}""",
+        """{"count": 0, "buckets": []}"""
+    ]
+    results = _MeasureFakePage(histograms)
+    actual = _ActualValues(results)
+    self.assertTrue('skip' in actual)
+    self.assertFalse('V8_DetachedContextAgeInGC' in actual)
+
+  def testWithData(self):
+    histograms = [
+        """{"count": 3, "buckets": [{"low": 1, "high": 2, "count": 1},
+                                    {"low": 2, "high": 3, "count": 2}]}""",
+        """{"count": 4, "buckets": [{"low": 1, "high": 2, "count": 2},
+                                    {"low": 2, "high": 3, "count": 2}]}""",
+    ]
+    results = _MeasureFakePage(histograms)
+    actual = _ActualValues(results)['V8_DetachedContextAgeInGC']
+    self.assertEqual(2, actual.value)
+    self.assertEqual('garbage_collections', actual.units)
+
+  def testWithSimplePage(self):
+    page_set = self.CreateEmptyPageSet()
+    page = SimplePage(page_set)
+    page_set.AddUserStory(page)
+    metric = v8_detached_context_age_in_gc.V8DetachedContextAgeInGC()
+    results = self.RunMeasurement(metric, page_set, options=self._options)
+    self.assertEquals(0, len(results.failures))
+    actual = _ActualValues(results)['V8_DetachedContextAgeInGC']
+    self.assertLessEqual(0, actual.value)
+    self.assertEqual('garbage_collections', actual.units)