Fix broken use lists in branch instructions.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
diff --git a/runtime/vm/flow_graph_optimizer.h b/runtime/vm/flow_graph_optimizer.h
index a5dce2dbac61a6e0effa8da69f16931e0e55d806..6918ca931771b099c2d4e6f118d37d25b38e5a20 100644
--- a/runtime/vm/flow_graph_optimizer.h
+++ b/runtime/vm/flow_graph_optimizer.h
@@ -21,6 +21,8 @@ class FlowGraphOptimizer : public FlowGraphVisitor {
         flow_graph_(flow_graph) { }
   virtual ~FlowGraphOptimizer() {}
 
+  FlowGraph* flow_graph() const { return flow_graph_; }
+
   // Use ICData to optimize, replace or eliminate instructions.
   void ApplyICData();