Add user_prefs and visitedlink components to GN build.

components/user_prefs/BUILD.gn

Index: components/user_prefs/BUILD.gn
diff --git a/components/user_prefs/BUILD.gn b/components/user_prefs/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..394c18f91d68611c9dd19f6a4359becddf4c4b61
--- /dev/null
+++ b/components/user_prefs/BUILD.gn
@@ -0,0 +1,20 @@
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+component("user_prefs") {
+  sources = [
+    "user_prefs.cc",
+    "user_prefs.h",
+    "user_prefs/user_prefs_export.h",
+  ]
+
+  defines = [ "USER_PREFS_IMPLEMENTATION" ]
+
+  deps = [
+    "//base",
+    "//base:prefs",
+    "//base/third_party/dynamic_annotations",
+    "//content/public/browser",
+  ]
+}