mac: Expose keychain access frequency to Telemetry.

base/mac/keychain_metrics.h

+// 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.
+
+#ifndef BASE_MAC_KEYCHAIN_METRICS_H_
+#define BASE_MAC_KEYCHAIN_METRICS_H_
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+
+namespace base {
+namespace mac {
+
+// Adds an entry to a local histogram to indicate that the keychain was
+// accessed. This function should be called each time the keychain is accessed
+// so that the number of entries in the histogram corresponds to the number of
+// times that the keychain is accessed.
+//
+// This local histogram is used by telemetry to track the number of times the
+// keychain is accessed.
+BASE_EXPORT void IncrementKeychainAccessHistogram();
+
+}  // namespace mac
+}  // namespace base
+
+#endif  // BASE_MAC_KEYCHAIN_METRICS_H_