Add a use list iterator that allows mutation of current.

runtime/vm/flow_graph_optimizer.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_FLOW_GRAPH_OPTIMIZER_H_
 #define VM_FLOW_GRAPH_OPTIMIZER_H_
 
 #include "vm/intermediate_language.h"
 #include "vm/flow_graph.h"
 
@@ skipping 68 matching lines @@
 
   void InsertAfter(Instruction* prev,
                    Instruction* instr,
                    Environment* env,
                    Definition::UseKind use_kind);
 
   void InsertConversionsFor(Definition* def);
 
   void InsertConversion(Representation from,
                         Representation to,
-                        Instruction* instr,
                         Value* use,
-                        Definition* def,
+                        Instruction* insert_before,
                         Instruction* deopt_target);
 
   bool InstanceCallNeedsClassCheck(InstanceCallInstr* call) const;
   bool MethodExtractorNeedsClassCheck(InstanceCallInstr* call) const;
 
   void InlineImplicitInstanceGetter(InstanceCallInstr* call);
   void InlineArrayLengthGetter(InstanceCallInstr* call,
                                intptr_t length_offset,
                                bool is_immutable,
                                MethodRecognizer::Kind kind);
@@ skipping 138 matching lines @@
 
   // Worklists of blocks and definitions.
   GrowableArray<BlockEntryInstr*> block_worklist_;
   GrowableArray<Definition*> definition_worklist_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_