Replace OStream with std::ostream.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 69f50b1beed5fbed238f7c711bc22f15aff12cff..9572a33ad87772595ef0f5f5d0d7e61f8071d15a 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <sstream>
+
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
@@ -360,9 +362,9 @@ LOperand* LPlatformChunk::GetNextSpillSlot(RegisterKind kind) {
 
 void LStoreNamedField::PrintDataTo(StringStream* stream) {
   object()->PrintTo(stream);
-  OStringStream os;
+  std::ostringstream os;
   os << hydrogen()->access() << " <- ";
-  stream->Add(os.c_str());
+  stream->Add(os.str().c_str());
   value()->PrintTo(stream);
 }