Improve some debug tools for mus.

services/ui/ws/ids.h

Index: services/ui/ws/ids.h
diff --git a/services/ui/ws/ids.h b/services/ui/ws/ids.h
index 0978e9c88c776369911179d56e96eaee0e3b6eed..a6268349313afe6001f54a0121f83b5a8c8bcccd 100644
--- a/services/ui/ws/ids.h
+++ b/services/ui/ws/ids.h
@@ -7,10 +7,12 @@
 
 #include <stdint.h>
 
+#include <string>
 #include <tuple>
 
 #include "base/containers/hash_tables.h"
 #include "base/hash.h"
+#include "base/strings/stringprintf.h"
 #include "services/ui/common/types.h"
 #include "services/ui/common/util.h"
 
@@ -51,6 +53,10 @@ struct WindowId {
            std::tie(other.client_id, other.window_id);
   }
 
+  std::string ToString() const {
+    return base::StringPrintf("%u:%u", client_id, window_id);
+  }
+
   ClientSpecificId client_id;
   ClientSpecificId window_id;
 };