[turbofan] Change map to vector in loop variable analysis.

src/compiler/loop-variable-optimizer.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_
 #define V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_
 
 #include "src/zone-containers.h"
 
 namespace v8 {
@@ skipping 88 matching lines @@
   InductionVariable* TryGetInductionVariable(Node* phi);
   void DetectInductionVariables(Node* loop);
 
   Graph* graph() { return graph_; }
   CommonOperatorBuilder* common() { return common_; }
   Zone* zone() { return zone_; }
 
   Graph* graph_;
   CommonOperatorBuilder* common_;
   Zone* zone_;
-  ZoneMap<int, const VariableLimits*> limits_;
+  ZoneVector<const VariableLimits*> limits_;
   ZoneMap<int, InductionVariable*> induction_vars_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_