Move operator<< for StringPiece into string_piece.{h,cc}

base/string_piece.h

Index: base/string_piece.h
diff --git a/base/string_piece.h b/base/string_piece.h
index e68302e466e2dc4a70f68fc5588d7e78ffae2ce5..7bce4ff8ca78e664c10b5b6bfd748873dbc92b01 100644
--- a/base/string_piece.h
+++ b/base/string_piece.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // Copied from strings/stringpiece.h with modifications
@@ -24,6 +24,7 @@
 #define BASE_STRING_PIECE_H_
 #pragma once
 
+#include <iosfwd>
 #include <string>
 
 #include "base/base_export.h"
@@ -399,6 +400,9 @@ inline bool operator>=(const StringPiece16& x, const StringPiece16& y) {
   return !(x < y);
 }
 
+BASE_EXPORT std::ostream& operator<<(std::ostream& o,
+                                     const StringPiece& piece);
+
 }  // namespace base
 
 // We provide appropriate hash functions so StringPiece and StringPiece16 can