[turbofan] Add streaming operator for opcodes to ease debugging.

src/compiler/opcodes.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/opcodes.h"
 
 #include <algorithm>
+#include <ostream>
 
 #include "src/base/macros.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 namespace {
 
 char const* const kMnemonics[] = {
 #define DECLARE_MNEMONIC(x) #x,
     ALL_OP_LIST(DECLARE_MNEMONIC)
 #undef DECLARE_MNEMONIC
         "UnknownOpcode"};
 
 }  // namespace
 
 
 // static
 char const* IrOpcode::Mnemonic(Value value) {
   size_t const n = std::min<size_t>(value, arraysize(kMnemonics) - 1);
   return kMnemonics[n];
 }
 
+
+std::ostream& operator<<(std::ostream& os, IrOpcode::Value opcode) {
+  return os << IrOpcode::Mnemonic(opcode);
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8