[sync] Add constexpr to EnumSet

components/reading_list/features/BUILD.gn

Index: components/reading_list/features/BUILD.gn
diff --git a/components/reading_list/features/BUILD.gn b/components/reading_list/features/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..948c8be01fdb90ac2be521a3608cc90978ec5fd7
--- /dev/null
+++ b/components/reading_list/features/BUILD.gn
@@ -0,0 +1,21 @@
+import("//build/buildflag_header.gni")
+import("//components/reading_list/features/reading_list.gni")
+
+buildflag_header("reading_list_enable_flags") {
+  header = "reading_list_enable_flags.h"
+  _enabled = is_ios && enable_reading_list
+  flags = [ "ENABLE_READING_LIST=$_enabled" ]
+}
+
+source_set("flags") {
+  sources = [
+    "reading_list_switches.cc",
+    "reading_list_switches.h",
+  ]
+  deps = [
+    "//base",
+  ]
+  public_deps = [
+    "//components/reading_list/features:reading_list_enable_flags",
+  ]
+}