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 507993196aeefde7c018114ef0e4951c9ed810d3..a4fe0be3306eae1737a505dd84d4cb640d5ac4e7 100644
--- a/components/os_crypt/os_crypt_mac.mm
+++ b/components/os_crypt/os_crypt_mac.mm
@@ -9,6 +9,7 @@
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "base/logging.h"
+#include "base/mac/keychain_metrics.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/lock.h"
@@ -57,6 +58,8 @@ crypto::SymmetricKey* GetEncryptionKey() {
 
   std::string password;
   if (use_mock_keychain || mock_keychain_command_line_flag) {
+    base::mac::IncrementKeychainAccessHistogram();
+
     password = "mock_password";
   } else {
     AppleKeychain keychain;