mac: Expose keychain access frequency to Telemetry.

tools/perf/metrics/keychain_metric.py

Index: tools/perf/metrics/keychain_metric.py
diff --git a/tools/perf/metrics/keychain_metric.py b/tools/perf/metrics/keychain_metric.py
new file mode 100644
index 0000000000000000000000000000000000000000..710d542e622f3089e69250aef4755529d3a90080
--- /dev/null
+++ b/tools/perf/metrics/keychain_metric.py
@@ -0,0 +1,44 @@
+# 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):

[jeremy, 2014/12/09 14:57:17]

I'd remove Mac from this and the other method name to match other Metrics.

[dtu, 2014/12/09 22:05:20]

Either way is fine to me.

[erikchen, 2014/12/13 02:39:58]

I intentionally changed the names to include the suffix Mac, as I explained to
dtu earlier in the reply chain. These methods only have an effect when run on
Macs. Naming these methods like the other Metrics will cause confusion, since
the other Metrics have an effect on all OSes. 

+    """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'])

[jeremy, 2014/12/09 14:57:17]

I guess nothing bad will happen if this is appended twice, I wonder if we should
just always launch Chrome with this option in Telemetry?

[dtu, 2014/12/09 22:05:20]

I think the AppendExtraBrowserArgs method removes duplicates. I like that it's
declared where it's being used.

[jeremy, 2014/12/10 05:35:18]

Good to know, please ignore my comment then :)

+
+  def AddResultsMac(self, tab, results):
+    """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