[ONOS-3642] Add missing meter icon in topology view

Change-Id: Iba1f10adf981b90fbc47ec649493436c7c50589c
diff --git a/core/api/src/main/java/org/onosproject/ui/topo/TopoConstants.java b/core/api/src/main/java/org/onosproject/ui/topo/TopoConstants.java
index e2034fa..63cbe4c 100644
--- a/core/api/src/main/java/org/onosproject/ui/topo/TopoConstants.java
+++ b/core/api/src/main/java/org/onosproject/ui/topo/TopoConstants.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 Open Networking Laboratory
+ * Copyright 2015,2016 Open Networking Laboratory
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -126,6 +126,9 @@
 
         public static final ButtonId SHOW_GROUP_VIEW =
                 new ButtonId("showGroupView");
+
+        public static final ButtonId SHOW_METER_VIEW =
+                new ButtonId("showMeterView");
     }
 
 }