Replace OStream with std::ostream.

src/compiler/instruction-codes.h

Index: src/compiler/instruction-codes.h
diff --git a/src/compiler/instruction-codes.h b/src/compiler/instruction-codes.h
index 4b7fe679e9a974aa8dee4013575d741f6bd6218e..0abed6c32181217e7d636d6dcee67b040297fce2 100644
--- a/src/compiler/instruction-codes.h
+++ b/src/compiler/instruction-codes.h
@@ -5,6 +5,8 @@
 #ifndef V8_COMPILER_INSTRUCTION_CODES_H_
 #define V8_COMPILER_INSTRUCTION_CODES_H_
 
+#include <iosfwd>
+
 #if V8_TARGET_ARCH_ARM
 #include "src/compiler/arm/instruction-codes-arm.h"
 #elif V8_TARGET_ARCH_ARM64
@@ -21,9 +23,6 @@
 
 namespace v8 {
 namespace internal {
-
-class OStream;
-
 namespace compiler {
 
 // Target-specific opcodes that specify which assembly sequence to emit.
@@ -46,7 +45,7 @@ enum ArchOpcode {
 #undef COUNT_ARCH_OPCODE
 };
 
-OStream& operator<<(OStream& os, const ArchOpcode& ao);
+std::ostream& operator<<(std::ostream& os, const ArchOpcode& ao);
 
 // Addressing modes represent the "shape" of inputs to an instruction.
 // Many instructions support multiple addressing modes. Addressing modes
@@ -65,12 +64,12 @@ enum AddressingMode {
 #undef COUNT_ADDRESSING_MODE
 };
 
-OStream& operator<<(OStream& os, const AddressingMode& am);
+std::ostream& operator<<(std::ostream& os, const AddressingMode& am);
 
 // The mode of the flags continuation (see below).
 enum FlagsMode { kFlags_none = 0, kFlags_branch = 1, kFlags_set = 2 };
 
-OStream& operator<<(OStream& os, const FlagsMode& fm);
+std::ostream& operator<<(std::ostream& os, const FlagsMode& fm);
 
 // The condition of flags continuation (see below).
 enum FlagsCondition {
@@ -94,7 +93,7 @@ enum FlagsCondition {
   kNotOverflow
 };
 
-OStream& operator<<(OStream& os, const FlagsCondition& fc);
+std::ostream& operator<<(std::ostream& os, const FlagsCondition& fc);
 
 // The InstructionCode is an opaque, target-specific integer that encodes
 // what code to emit for an instruction in the code generator. It is not