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

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 10183565a9362c01cb6335fa0c489dd0f55e180c..56717e0e20702bb34512805dec63c2de08f3ac09 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -193,9 +193,8 @@ static bool CompileParsedFunctionHelper(const ParsedFunction& parsed_function,
         FlowGraphTypePropagator propagator(*flow_graph);
         propagator.PropagateTypes();
 
-        // TODO(zerny): Here we assume that the use lists remain valid after
-        // type propagation. We should construct a use-list validator to make
-        // this explicit in DEBUG mode.
+        // Verify that the use lists are still valid.
+        DEBUG_ASSERT(flow_graph->ValidateUseLists());
 
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();