[turbofan] More const-correctness changes.

src/compiler/simplified-operator-reducer.cc

 // Copyright 2014 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.
 
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/simplified-operator-reducer.h"
 
@@ skipping 81 matching lines @@
       break;
     }
     default:
       break;
   }
   return NoChange();
 }
 
 
 Reduction SimplifiedOperatorReducer::Change(Node* node, Operator* op, Node* a) {
-  graph()->ChangeOperator(node, op);
+  node->set_op(op);
   node->ReplaceInput(0, a);
   return Changed(node);
 }
 
 
 Reduction SimplifiedOperatorReducer::ReplaceFloat64(double value) {
   return Replace(jsgraph()->Float64Constant(value));
 }
 
 
@@ skipping 15 matching lines @@
 Graph* SimplifiedOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 
 Heap* SimplifiedOperatorReducer::heap() const {
   return jsgraph()->isolate()->heap();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8