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

content/test/test_content_client.cc

 // 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.
 
 #include "content/test/test_content_client.h"
 
 #include "base/base_paths.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/path_service.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 
 namespace content {
 
 TestContentClient::TestContentClient()
     : data_pack_(ui::SCALE_FACTOR_100P) {
   // content_resources.pak is not built on iOS as it is not required.
 #if !defined(OS_IOS)
   base::FilePath content_resources_pack_path;
 #if defined(OS_ANDROID)
   // on Android all pak files are inside the paks folder.
@@ skipping 18 matching lines @@
 
 base::StringPiece TestContentClient::GetDataResource(
     int resource_id,
     ui::ScaleFactor scale_factor) const {
   base::StringPiece resource;
   data_pack_.GetStringPiece(resource_id, &resource);
   return resource;
 }
 
 }  // namespace content