OSCrypt for POSIX uses libsecret to store a randomised encryption key.

components/os_crypt/os_crypt.h

Index: components/os_crypt/os_crypt.h
diff --git a/components/os_crypt/os_crypt.h b/components/os_crypt/os_crypt.h
index ecffa4e5ed4c8c81b4acde3b8169b156eb305f51..a65064e88fe9275eb8568d02a50e5f4c0afe1908 100644
--- a/components/os_crypt/os_crypt.h
+++ b/components/os_crypt/os_crypt.h
@@ -11,6 +11,10 @@
 #include "base/strings/string16.h"
 #include "build/build_config.h"
 
+#if defined(USE_LIBSECRET)
+#include "components/os_crypt/key_storage_linux.h"
+#endif
+
 // The OSCrypt class gives access to simple encryption and decryption of
 // strings. Note that on Mac, access to the system Keychain is required and
 // these calls can block the current thread to collect user input.
@@ -47,4 +51,16 @@ class OSCrypt {
   DISALLOW_IMPLICIT_CONSTRUCTORS(OSCrypt);
 };
 
+#if defined(USE_LIBSECRET) && defined(UNIT_TEST)
+// For unit testing purposes, inject methods to be used.
+// |get_key_storage_mock| provides the desired |KeyStorage| implementation.
+// If the provider returns |nullptr|, a hardcoded password will be used.
+// |get_password_v11_mock| provides a password to derive the encryption key from
+// If |use| is true, the provided values will be injected. Otherwise, the
+// real implementation is restored.
+void UseMockKeyStorageForTesting(bool use,

[Lei Zhang, 2016/05/19 22:45:38]

You probably don't need |use| - you can indicate use = false with both function
pointers being nullptr.

[cfroussios, 2016/05/20 16:44:52]

Done.

+                                 KeyStorageLinux* (*get_key_storage_mock)(),
+                                 std::string* (*get_password_v11_mock)());
+#endif  // defined(USE_LIBSECRET) && defined(UNIT_TEST)
+
 #endif  // COMPONENTS_OS_CRYPT_OS_CRYPT_H_