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

src/compiler/opcodes.h

Index: src/compiler/opcodes.h
diff --git a/src/compiler/opcodes.h b/src/compiler/opcodes.h
index 270b73f294926ca9f8585e086086ac59cff9aa71..5ccbe4e1ebb9ef339a4e922beb3258fa433e4119 100644
--- a/src/compiler/opcodes.h
+++ b/src/compiler/opcodes.h
@@ -5,6 +5,8 @@
 #ifndef V8_COMPILER_OPCODES_H_
 #define V8_COMPILER_OPCODES_H_
 
+#include <iosfwd>
+
 // Opcodes for control operators.
 #define CONTROL_OP_LIST(V) \
   V(Start)                 \
@@ -348,6 +350,8 @@ class IrOpcode {
   }
 };
 
+std::ostream& operator<<(std::ostream&, IrOpcode::Value);
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8