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

src/compiler/opcodes.cc

Index: src/compiler/opcodes.cc
diff --git a/src/compiler/opcodes.cc b/src/compiler/opcodes.cc
index 1c94c19c780fec8c167a0b4a5bf2277c89bd7d89..2a8e01a26d90e9bfbe4460f015358e13eb2f8be8 100644
--- a/src/compiler/opcodes.cc
+++ b/src/compiler/opcodes.cc
@@ -5,6 +5,7 @@
 #include "src/compiler/opcodes.h"
 
 #include <algorithm>
+#include <ostream>
 
 #include "src/base/macros.h"
 
@@ -29,6 +30,11 @@ char const* IrOpcode::Mnemonic(Value value) {
   return kMnemonics[n];
 }
 
+
+std::ostream& operator<<(std::ostream& os, IrOpcode::Value opcode) {
+  return os << IrOpcode::Mnemonic(opcode);
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8