mac: Expose keychain access frequency to Telemetry.

components/os_crypt/os_crypt_mac.mm

Index: components/os_crypt/os_crypt_mac.mm
diff --git a/components/os_crypt/os_crypt_mac.mm b/components/os_crypt/os_crypt_mac.mm
index ab19283c2797921891e5a13a237e94e80d624712..8b0de1478c0c16a5481328b92f349ccfabb44844 100644
--- a/components/os_crypt/os_crypt_mac.mm
+++ b/components/os_crypt/os_crypt_mac.mm
@@ -10,6 +10,7 @@
 #include "base/debug/leak_annotations.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/perf_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/lock.h"
 #include "components/os_crypt/keychain_password_mac.h"
@@ -57,6 +58,8 @@ crypto::SymmetricKey* GetEncryptionKey() {
 
   std::string password;
   if (use_mock_keychain || mock_keychain_command_line_flag) {
+    base::IncrementKeychainAccessHistogram();
+
     password = "mock_password";
   } else {
     AppleKeychain keychain;