net: Update the include paths of base/string_piece.h to its new location.

net/http/http_request_headers.h

 // 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.
 //
 // HttpRequestHeaders manages the request headers.
 // It maintains these in a vector of header key/value pairs, thereby maintaining
 // the order of the headers.  This means that any lookups are linear time
 // operations.
 
 #ifndef NET_HTTP_HTTP_REQUEST_HEADERS_H_
 #define NET_HTTP_HTTP_REQUEST_HEADERS_H_
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "net/base/net_export.h"
 #include "net/base/net_log.h"
 
 namespace net {
 
 class NET_EXPORT HttpRequestHeaders {
  public:
   struct HeaderKeyValuePair {
     HeaderKeyValuePair();
     HeaderKeyValuePair(const base::StringPiece& key,
@@ skipping 140 matching lines @@
   // Allow the copy construction and operator= to facilitate copying in
   // HttpRequestHeaders.
   // TODO(willchan): Investigate to see if we can remove the need to copy
   // HttpRequestHeaders.
   // DISALLOW_COPY_AND_ASSIGN(HttpRequestHeaders);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_REQUEST_HEADERS_H_