[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..2904d9b9b2b4f30f13aa6cbae65a6b774514bd4c
--- /dev/null
+++ b/tools/perf/measurements/v8_detached_context_age_in_gc_unittest.py
@@ -0,0 +1,84 @@
+# 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.results import page_test_results
+from telemetry.unittest_util import options_for_unittests
+from telemetry.unittest_util import page_test_test_case
+
+
+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(list(
+      (v.name, (v.units, v.value))
+      for v in results.all_page_specific_values
+      ))
+
+
+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)
+    expected = {'V8_DetachedContextAgeInGC': ('garbage_collections', 0) }
+    self._AssertResultsEqual(expected, _ActualValues(results))
+
+  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)
+    expected = {'V8_DetachedContextAgeInGC': ('garbage_collections', 2) }
+    self._AssertResultsEqual(expected, _ActualValues(results))
+
+  def _AssertResultsEqual(self, expected, actual):
+    for key in expected.iterkeys():
+      self.assertIn(key, actual.keys())
+      self.assertEqual(expected[key], actual[key],
+          'Result for [' + key + '] - expected ' + str(expected[key]) +
+          ' but got ' + str(actual[key]))