Replace OStream with std::ostream.

src/compiler/machine-type.h

Index: src/compiler/machine-type.h
diff --git a/src/compiler/machine-type.h b/src/compiler/machine-type.h
index 88b482c80422ba47e03b29c71ce1dbaa93934840..059b058563f5dcb47cdb7bf67036c25846224e73 100644
--- a/src/compiler/machine-type.h
+++ b/src/compiler/machine-type.h
@@ -5,15 +5,14 @@
 #ifndef V8_COMPILER_MACHINE_TYPE_H_
 #define V8_COMPILER_MACHINE_TYPE_H_
 
+#include <iosfwd>
+
 #include "src/base/bits.h"
 #include "src/globals.h"
 #include "src/zone.h"
 
 namespace v8 {
 namespace internal {
-
-class OStream;
-
 namespace compiler {
 
 // Machine-level types and representations.
@@ -54,7 +53,7 @@ enum MachineType {
   kMachAnyTagged = kRepTagged | kTypeAny
 };
 
-OStream& operator<<(OStream& os, const MachineType& type);
+std::ostream& operator<<(std::ostream& os, const MachineType& type);
 
 typedef uint16_t MachineTypeUnion;