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

components/os_crypt/BUILD.gn

Index: components/os_crypt/BUILD.gn
diff --git a/components/os_crypt/BUILD.gn b/components/os_crypt/BUILD.gn
index e283deae0881d16e8277ebeadf54de93eb238223..6500f60e5bc3365480d19c496a46bf1cca4b912a 100644
--- a/components/os_crypt/BUILD.gn
+++ b/components/os_crypt/BUILD.gn
@@ -44,9 +44,15 @@ source_set("os_crypt") {
   }
 
   if (is_desktop_linux && use_glib) {
+    sources -= [ "os_crypt_posix.cc" ]
     sources += [
-      "libsecret_util_posix.cc",
-      "libsecret_util_posix.h",
+      "key_storage_libsecret.cc",
+      "key_storage_libsecret.h",
+      "key_storage_linux.cc",
+      "key_storage_linux.h",
+      "libsecret_util_linux.cc",
+      "libsecret_util_linux.h",
+      "os_crypt_linux.cc",
     ]
     configs += [ "//build/config/linux:glib" ]
     deps += [ "//third_party/libsecret" ]
@@ -67,4 +73,14 @@ source_set("unit_tests") {
     "//crypto",
     "//testing/gtest",
   ]
+
+  if (is_desktop_linux) {
+    sources += [
+      "os_crypt_mocker_linux.cc",
+      "os_crypt_mocker_linux.h",
+      "os_crypt_util_linux_unittest.cc",
+    ]
+    deps += [ "//third_party/libsecret" ]
+    defines = [ "USE_LIBSECRET" ]
+  }
 }