Revert r20998.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
===================================================================
--- runtime/vm/flow_graph_optimizer.h	(revision 20999)
+++ runtime/vm/flow_graph_optimizer.h	(working copy)
@@ -16,11 +16,9 @@
 
 class FlowGraphOptimizer : public FlowGraphVisitor {
  public:
-  FlowGraphOptimizer(FlowGraph* flow_graph,
-                     GrowableArray<Field*>* guarded_fields)
+  explicit FlowGraphOptimizer(FlowGraph* flow_graph)
       : FlowGraphVisitor(flow_graph->reverse_postorder()),
-        flow_graph_(flow_graph),
-        guarded_fields_(guarded_fields) { }
+        flow_graph_(flow_graph) { }
   virtual ~FlowGraphOptimizer() {}
 
   FlowGraph* flow_graph() const { return flow_graph_; }
@@ -160,7 +158,6 @@
                                     Definition* right_instr);
 
   FlowGraph* flow_graph_;
-  GrowableArray<Field*>* guarded_fields_;
 
   DISALLOW_COPY_AND_ASSIGN(FlowGraphOptimizer);
 };