Disallow clicking on [merged].

The current behaviour is confusing. Eventually we want to expand to the
set of nodes that were nodes, but for now this improves things.

Bug: 148596659
Change-Id: Ib67c3fe72d7c01d5fe21598081add74471d72ce1
diff --git a/ui/src/controller/heap_profile_controller.ts b/ui/src/controller/heap_profile_controller.ts
index 2f3b07d..9e26d8a 100644
--- a/ui/src/controller/heap_profile_controller.ts
+++ b/ui/src/controller/heap_profile_controller.ts
@@ -234,8 +234,16 @@
       // Instead of hash, we will store index of callsite in this original array
       // as an id of callsite. That way, we have quicker access to parent and it
       // will stay unique.
-      flamegraphData.push(
-          {id: i, totalSize, depth, parentId, name, selfSize, mapping});
+      flamegraphData.push({
+        id: i,
+        totalSize,
+        depth,
+        parentId,
+        name,
+        selfSize,
+        mapping,
+        merged: false
+      });
     }
     return flamegraphData;
   }