mac: Expose keychain access frequency to Telemetry.

tools/perf/metrics/keychain_metric.py

+# Copyright 2014 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 sys
+
+from metrics import Metric
+from telemetry.value import histogram_util
+from telemetry.value import scalar
+
+
+class KeychainMetric(Metric):
+  """KeychainMetric gathers keychain statistics from the browser object.
+
+  This includes the number of times that the keychain was accessed.
+  """
+
+  DISPLAY_NAME = 'OSX_Keychain_Access'
+  HISTOGRAM_NAME = 'OSX.Keychain.Access'
+
+  @classmethod
+  def CustomizeBrowserOptionsMac(cls, options):
+    """Adds a browser argument that allows for the collection of keychain
+    metrics. Has no effect on non-Mac platforms."""
+    if sys.platform != 'darwin':
+      return
+
+    options.AppendExtraBrowserArgs(['--enable-stats-collection-bindings'])
+
+  def AddResultsMac(self, tab, results):

[jeremy, 2014/12/14 08:55:50]

I feel quite strongly that these should just be called
AddResults/CustomizeBrowserOptions - I think the platform constraints are clear
from the class name.

Having said that I'm not an owner so dtu gets the final say.

+    """Adds the number of times that the keychain was accessed to |results|.
+    Has no effect on non-Mac platforms."""
+    if sys.platform != 'darwin':
+      return
+
+    access_count = histogram_util.GetHistogramSum(
+        histogram_util.BROWSER_HISTOGRAM, KeychainMetric.HISTOGRAM_NAME, tab)
+    results.AddValue(scalar.ScalarValue(
+        results.current_page, KeychainMetric.DISPLAY_NAME, 'count',
+        access_count))
+
+  def AddResults(self, tab, results):
+    """This method should never be called."""
+    assert False