Enable RL sync by default on iOS

components/reading_list/core/BUILD.gn

Index: components/reading_list/core/BUILD.gn
diff --git a/components/reading_list/proto/BUILD.gn b/components/reading_list/core/BUILD.gn
similarity index 59%
copy from components/reading_list/proto/BUILD.gn
copy to components/reading_list/core/BUILD.gn
index 927a5eea83e167675b2cb6fee3186b0fced0cffa..52dbc37326d1c354765936715725ca02e3978b5f 100644
--- a/components/reading_list/proto/BUILD.gn
+++ b/components/reading_list/core/BUILD.gn
@@ -2,13 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//third_party/protobuf/proto_library.gni")
-
-proto_library("proto") {
+source_set("core") {
   sources = [
-    "reading_list.proto",
+    "reading_list_switches.cc",
+    "reading_list_switches.h",
   ]
   deps = [
-    "//components/sync/protocol",
+    "//base",
   ]
 }