Replace OStream with std::ostream.

src/disassembler.h

 // Copyright 2006-2008 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_DISASSEMBLER_H_
 #define V8_DISASSEMBLER_H_
 
 #include "src/allocation.h"
 
 namespace v8 {
 namespace internal {
 
 class Disassembler : public AllStatic {
  public:
   // Decode instructions in the the interval [begin, end) and print the
   // code into os. Returns the number of bytes disassembled or 1 if no
   // instruction could be decoded.
   // the code object is used for name resolution and may be null.
-  static int Decode(Isolate* isolate, OStream* os, byte* begin, byte* end,
+  static int Decode(Isolate* isolate, std::ostream* os, byte* begin, byte* end,
                     Code* code = NULL);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_DISASSEMBLER_H_