Replace OStream with std::ostream.

src/compiler/graph-visualizer.h

 // Copyright 2013 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.
 
 #ifndef V8_COMPILER_GRAPH_VISUALIZER_H_
 #define V8_COMPILER_GRAPH_VISUALIZER_H_
 
-#include "src/v8.h"
+#include <iosfwd>
 
 namespace v8 {
 namespace internal {
-
-class OStream;
-
 namespace compiler {
 
 class Graph;
 
 struct AsDOT {
   explicit AsDOT(const Graph& g) : graph(g) {}
   const Graph& graph;
 };
 
-OStream& operator<<(OStream& os, const AsDOT& ad);
+std::ostream& operator<<(std::ostream& os, const AsDOT& ad);
+
 
 struct AsJSON {
   explicit AsJSON(const Graph& g) : graph(g) {}
   const Graph& graph;
 };
 
-OStream& operator<<(OStream& os, const AsJSON& ad);
-}
-}
-}  // namespace v8::internal::compiler
+std::ostream& operator<<(std::ostream& os, const AsJSON& ad);
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_COMPILER_GRAPH_VISUALIZER_H_