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..243bb2c2dc269d2e30def360f30d530a572dbe6d 100644
--- a/components/os_crypt/os_crypt.h
+++ b/components/os_crypt/os_crypt.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "build/build_config.h"
+#include "components/os_crypt/key_storage_linux.h"

[vabr (Chromium), 2016/05/13 15:10:18]

You should #include this file unconditionally if you only put it in build
dependencies on Linux. You could enclose it in the same #ifdef as
UseMockKeyStorage below, but instead I suggest separating these newly added
parts in os_crypt_linux.h and then making os_crypt_linux.h include os_crypt.h
and only referencing os_crypt_linux.h from os_crypt_linux.cc.

[cfroussios, 2016/05/13 17:09:12]

Right now, the entry-point to OSCrypt is this file for any build. I think that
duplicating the entire declaration for just 2 conditional lines is too high a
price, especially since we're not solving mac's conditional lines. That said,
the declaration itself is also small, so I do not insist.

 
 // The OSCrypt class gives access to simple encryption and decryption of
 // strings. Note that on Mac, access to the system Keychain is required and
@@ -43,6 +44,10 @@ class OSCrypt {
   static void UseMockKeychain(bool use_mock);
 #endif
 
+#if defined(USE_LIBSECRET)
+  static KeyStorageMock* UseMockKeyStorage(bool use_mock);

[vabr (Chromium), 2016/05/13 15:10:18]

nit: Please describe what the method does.

[cfroussios, 2016/05/13 17:09:12]

Done.

+#endif
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(OSCrypt);
 };