Revert "Remove unassigned event log tags feature"

Revert submission 3400623-remove_unassigned_event_log_tags

Reason for revert: Droidmonitor created revert due to b/383362497. Will be verifying through ABTD before submission.

Reverted changes: /q/submissionid:3400623-remove_unassigned_event_log_tags

Change-Id: I1378364ff5f9c6f09f47d72c104ae603e0d2063a
diff --git a/android/logtags.go b/android/logtags.go
index 1e92dad..7929057 100644
--- a/android/logtags.go
+++ b/android/logtags.go
@@ -16,8 +16,41 @@
 
 import "github.com/google/blueprint"
 
+func init() {
+	RegisterParallelSingletonType("logtags", LogtagsSingleton)
+}
+
 type LogtagsInfo struct {
 	Logtags Paths
 }
 
 var LogtagsProviderKey = blueprint.NewProvider[*LogtagsInfo]()
+
+func LogtagsSingleton() Singleton {
+	return &logtagsSingleton{}
+}
+
+type logtagsSingleton struct{}
+
+func MergedLogtagsPath(ctx PathContext) OutputPath {
+	return PathForIntermediates(ctx, "all-event-log-tags.txt")
+}
+
+func (l *logtagsSingleton) GenerateBuildActions(ctx SingletonContext) {
+	var allLogtags Paths
+	ctx.VisitAllModules(func(module Module) {
+		if !module.ExportedToMake() {
+			return
+		}
+		if logtagsInfo, ok := OtherModuleProvider(ctx, module, LogtagsProviderKey); ok {
+			allLogtags = append(allLogtags, logtagsInfo.Logtags...)
+		}
+	})
+
+	builder := NewRuleBuilder(pctx, ctx)
+	builder.Command().
+		BuiltTool("merge-event-log-tags").
+		FlagWithOutput("-o ", MergedLogtagsPath(ctx)).
+		Inputs(SortedUniquePaths(allLogtags))
+	builder.Build("all-event-log-tags.txt", "merge logtags")
+}
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index cd3808c..b9cb076 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -878,7 +878,8 @@
 	eventLogtagsPath := etcPath.Join(ctx, "event-log-tags")
 	builder.Command().Text("mkdir").Flag("-p").Text(etcPath.String())
 	cmd := builder.Command().BuiltTool("merge-event-log-tags").
-		FlagWithArg("-o ", eventLogtagsPath.String())
+		FlagWithArg("-o ", eventLogtagsPath.String()).
+		FlagWithInput("-m ", android.MergedLogtagsPath(ctx))
 
 	for _, path := range android.SortedKeys(logtagsFilePaths) {
 		cmd.Text(path)