[turbofan] Make sure Operator is really immutable.

src/compiler/node-matchers.h

 // 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.
 
 #ifndef V8_COMPILER_NODE_MATCHERS_H_
 #define V8_COMPILER_NODE_MATCHERS_H_
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/node.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // A pattern matcher for nodes.
 struct NodeMatcher {
   explicit NodeMatcher(Node* node) : node_(node) {}
 
   Node* node() const { return node_; }
-  Operator* op() const { return node()->op(); }
+  const Operator* op() const { return node()->op(); }
   IrOpcode::Value opcode() const { return node()->opcode(); }
 
   bool HasProperty(Operator::Property property) const {
     return op()->HasProperty(property);
   }
   Node* InputAt(int index) const { return node()->InputAt(index); }
 
 #define DEFINE_IS_OPCODE(Opcode) \
   bool Is##Opcode() const { return opcode() == IrOpcode::k##Opcode; }
   ALL_OP_LIST(DEFINE_IS_OPCODE)
@@ skipping 106 matching lines @@
 typedef BinopMatcher<Int32Matcher, Int32Matcher> Int32BinopMatcher;
 typedef BinopMatcher<Uint32Matcher, Uint32Matcher> Uint32BinopMatcher;
 typedef BinopMatcher<Int64Matcher, Int64Matcher> Int64BinopMatcher;
 typedef BinopMatcher<Uint64Matcher, Uint64Matcher> Uint64BinopMatcher;
 typedef BinopMatcher<Float64Matcher, Float64Matcher> Float64BinopMatcher;
 }
 }
 }  // namespace v8::internal::compiler
 
 #endif  // V8_COMPILER_NODE_MATCHERS_H_