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

components/os_crypt/os_crypt_unittest.cc

Index: components/os_crypt/os_crypt_unittest.cc
diff --git a/components/os_crypt/os_crypt_unittest.cc b/components/os_crypt/os_crypt_unittest.cc
index 9837cbc29a0d8d1725056fdd79006e3e9e54e2ed..a9aec3a835d8d3e75cf279984458b5e24b9d944e 100644
--- a/components/os_crypt/os_crypt_unittest.cc
+++ b/components/os_crypt/os_crypt_unittest.cc
@@ -23,6 +23,9 @@ class OSCryptTest : public testing::Test {
 #if defined(OS_MACOSX)
     OSCrypt::UseMockKeychain(true);
 #endif
+#if defined(USE_LIBSECRET)
+    OSCrypt::UseMockKeyStorage(true);
+#endif
   }
 
  private: