Restore r20998 with a bug fix: add field to guarded_fields_ when it contains relevant cid. Was miss…

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
===================================================================
--- runtime/vm/flow_graph_optimizer.h	(revision 21001)
+++ runtime/vm/flow_graph_optimizer.h	(working copy)
@@ -16,9 +16,11 @@
 
 class FlowGraphOptimizer : public FlowGraphVisitor {
  public:
-  explicit FlowGraphOptimizer(FlowGraph* flow_graph)
+  FlowGraphOptimizer(FlowGraph* flow_graph,
+                     GrowableArray<Field*>* guarded_fields)
       : FlowGraphVisitor(flow_graph->reverse_postorder()),
-        flow_graph_(flow_graph) { }
+        flow_graph_(flow_graph),
+        guarded_fields_(guarded_fields) { }
   virtual ~FlowGraphOptimizer() {}
 
   FlowGraph* flow_graph() const { return flow_graph_; }
@@ -157,7 +159,10 @@
                                     Definition* left_instr,
                                     Definition* right_instr);
 
+  void AddToGuardedFields(Field* field);
+
   FlowGraph* flow_graph_;
+  GrowableArray<Field*>* guarded_fields_;
 
   DISALLOW_COPY_AND_ASSIGN(FlowGraphOptimizer);
 };