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

net/dns/dns_transaction.h

Index: net/dns/dns_transaction.h
diff --git a/net/dns/dns_transaction.h b/net/dns/dns_transaction.h
index e6a1d029d934211afcb455c80f021b4d393679e2..443cfaec3996f85e4122f0d3149220a33b4a9970 100644
--- a/net/dns/dns_transaction.h
+++ b/net/dns/dns_transaction.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.
 
@@ -11,6 +11,7 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/string_piece.h"
 #include "base/timer.h"
 #include "base/threading/non_thread_safe.h"
 #include "net/base/completion_callback.h"