Replace std::unordered_set with std::set.

Per //base/containers/README.md, std::set is generally recommended,
unless there are strong reasons for using unordered_set.

Change-Id: Id6fa60482aa4277f723137bbc53d3b7fa341e925
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2372464Reviewed-by: Joanmarie Diggs <jdiggs@igalia.com>
Commit-Queue: Jacobo Aragunde Pérez <jaragunde@igalia.com>
Cr-Commit-Position: refs/heads/master@{#801409}

ui/accessibility/platform/atk_util_auralinux.cc

@@ -5,6 +5,7 @@
 #include <atk/atk.h>
 #include <map>
 #include <memory>
+#include <set>
 #include <string>
 #include <utility>
 
@@ -53,7 +54,7 @@ static KeySnoopFuncMap& GetActiveKeySnoopFunctions() {
   return *active_key_snoop_functions;
 }
 
-using AXPlatformNodeSet = std::unordered_set<ui::AXPlatformNodeAuraLinux*>;
+using AXPlatformNodeSet = std::set<ui::AXPlatformNodeAuraLinux*>;
 static AXPlatformNodeSet& GetNodesWithPostponedEvents() {
   static base::NoDestructor<AXPlatformNodeSet> nodes_with_postponed_events_list;
   return *nodes_with_postponed_events_list;