Validate well-formedness of the use lists in debug mode.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
diff --git a/runtime/vm/flow_graph_optimizer.cc b/runtime/vm/flow_graph_optimizer.cc
index 6d1d27a158749a2b7c945b49d21455f6ab30cd89..fb27ba1dddd950d224fd0d0a458b4c3963ec5579 100644
--- a/runtime/vm/flow_graph_optimizer.cc
+++ b/runtime/vm/flow_graph_optimizer.cc
@@ -154,6 +154,7 @@ static void RemovePushArguments(InstanceCallComp* comp) {
   // Remove original push arguments.
   for (intptr_t i = 0; i < comp->ArgumentCount(); ++i) {
     PushArgumentInstr* push = comp->ArgumentAt(i);
+    push->ReplaceUsesWith(push->value());
     push->RemoveFromGraph();
   }
 }