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

webkit/fileapi/file_system_dir_url_request_job_unittest.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 "webkit/fileapi/file_system_dir_url_request_job.h"
 
 #include <string>
 
 #include "base/files/file_path.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/format_macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop.h"
 #include "base/platform_file.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/utf_string_conversions.h"
 #include "net/base/net_errors.h"
 #include "net/base/net_util.h"
 #include "net/http/http_request_headers.h"
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_test_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/icu/public/i18n/unicode/regex.h"
 #include "webkit/fileapi/external_mount_points.h"
@@ skipping 261 matching lines @@
   CreateDirectory("foo");
   TestRequestNoRun(CreateFileSystemURL("foo/"));
   // Run StartAsync() and only StartAsync().
   MessageLoop::current()->DeleteSoon(FROM_HERE, request_.release());
   MessageLoop::current()->RunUntilIdle();
   // If we get here, success! we didn't crash!
 }
 
 }  // namespace (anonymous)
 }  // namespace fileapi