Enable RL by default

components/reading_list/core/BUILD.gn

Index: components/reading_list/core/BUILD.gn
diff --git a/components/reading_list/core/BUILD.gn b/components/reading_list/core/BUILD.gn
index 52dbc37326d1c354765936715725ca02e3978b5f..f45b10c0b421a0dfb83bfe035648d24655d0c021 100644
--- a/components/reading_list/core/BUILD.gn
+++ b/components/reading_list/core/BUILD.gn
@@ -2,12 +2,22 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/buildflag_header.gni")
+import("//components/reading_list/core/reading_list.gni")
+
 source_set("core") {
   sources = [
     "reading_list_switches.cc",
     "reading_list_switches.h",
   ]
   deps = [
+    ":reading_list_enable_flags",
     "//base",
   ]
 }
+
+buildflag_header("reading_list_enable_flags") {
+  header = "reading_list_enable_flags.h"
+  _enabled = is_ios && enable_reading_list
+  flags = [ "ENABLE_READING_LIST=$_enabled" ]
+}